🎁 A friend invited you: ₹200 off the full road. It applies automatically when you unlock in the game.
PREPFLIX Play village 1 free
The Lantern Road · 30-day system design challenge

Finish 29 system design villages in 30 days. Get every rupee back and a referral.

A game that teaches system design. Walk village maps, learn from mentors, and win battles built on real trade-offs: rate limiters, consistent hashing, message queues, payments and more. It covers every chapter of both System Design Interview volumes.

▶ Play village 1 free How the challenge works

Sign in with Google · no card needed to start · Prepflix students get everything included

A battle in the cache workshop: build the system by placing components in order
BUILD THE SYSTEMTURN 3 / 5
29villages
87buildings to restore
29boss battles
1,231challenge variants
2SDI volumes covered
In one paragraph

What is The Lantern Road?

The Lantern Road is a browser game that teaches system design for software engineering interviews. It is made by Prepflix, an Indian interview-prep program founded by Pranjal Jain (IIT Kanpur, ex-Microsoft). You travel through 29 villages; each one is a classic system design problem such as a rate limiter, consistent hashing, a URL shortener, a chat system, a message queue or a payment system. In every village you learn the concept from a mentor, then win battles where you trace requests, debug incidents, size capacity and build the system in the right order. The first village is free with a Google sign-in. The full road costs ₹999 once, and players who finish all 29 villages within 30 days of paying get a full refund (or ₹2,000 off the Prepflix course) plus a referral at a company they choose.

Last updated October 2026 · Built for engineers preparing for SDE-2, senior and backend interviews at product companies.

How it works

Start free. Commit for 30 days. Finish and get paid back.

01

Play the first village free

Sign in with Google and restore Willowmere: requests, storage and caching. Three buildings, a boss, no payment.

02

Unlock the road for ₹999

One payment unlocks all 29 villages and the full field guide. Your 30-day clock starts the moment you pay.

03

Finish in 30 days, claim it all

Restore every village before your deadline, then walk us through one design on a 20-minute call. Take your money back or ₹2,000 off the full course, plus a referral at a company you choose and a certificate for LinkedIn.

The challenge

We bet you can finish. If you do, it costs you nothing.

Most people buy a system design course and stop at chapter three. The ₹999 is a commitment device. Keep your promise to yourself and you get it back.

  • Your choice of reward: a full refund to your original payment method, or ₹2,000 off the full Prepflix course
  • A referral for a role at the company you choose, through our network of mentors and alumni
  • A real conversation: the verification call is a mini design review with our team
Full road
₹999
one-time · all 29 villages
₹0 if you finish within 30 days
Invited by a friend? ₹799.
Start free, unlock in-game UPI, cards and netbanking via Razorpay. Challenge terms
Inside the game

No videos to sit through. Every concept is a battle you win.

Observatory battle: trace a request through DNS, load balancer, cache and database

Trace the request

Follow a request through DNS, load balancers, caches and databases, stop by stop.

Library battle: inspect incident evidence and choose the fix

Investigate the failure

Inspect the evidence from a real-looking incident, then choose the fix that keeps the guarantee.

Boss battle on the moonlit bridge mixing concepts from earlier villages

Beat the village boss

Ten mixed encounters that pull in concepts from earlier villages. You need 80% to open the bridge.

🎁

Bring a friend: you both get ₹200 off

Every player gets an invite link in the game. Your friend pays ₹799 instead of ₹999. When they pay, you get ₹200 too: off your own unlock, or back to your card if you’ve already paid. That’s up to ₹800 across four friends.

🎓

A certificate worth posting

Finish the road and you get a verifiable certificate page with a credential ID. Add it to your LinkedIn profile in one click, or share it to your feed.

The road

29 villages. Every chapter of both volumes.

Original lessons and scenarios aligned with the chapter topics of Alex Xu’s System Design Interview Volumes 1 and 2. This is an independent learning game, not an official companion.

1WillowmereScale from zero to millions
2Sunstone CrossingBack-of-the-envelope estimation
3Council of EmbersSystem design interview framework
4TokenwatchRate limiter
5RinghavenConsistent hashing
6MemorydeltaKey-value store
7ClockforgeDistributed unique IDs
8AliasportURL shortener
9WebwealdWeb crawler
10BellharborNotification system
11StorybrookNews feed system
12WhisperbridgeChat system
13PrefixgroveSearch autocomplete
14SilverreelVideo platform
15CloudhavenCloud file synchronization
16The Return SchoolThe learning continues
17NearleafProximity service
18Firefly MeadowNearby friends
19Wayfarer PassMaps and navigation
20LogportDistributed message queue
21SignalpeakMetrics monitoring
22ClickwaterAd click event aggregation
23Lastroom InnHotel reservation
24PostlightDistributed email service
25ObjectreachS3-like object storage
26ScorefallReal-time gaming leaderboard
27PayhavenPayment system
28LedgerdeepDigital wallet
29The Lantern CitadelStock exchange
The mentors of the Lantern Road
Already a Prepflix student?

It’s already yours.

Enrolled Prepflix students get the full Lantern Road at no cost. Sign in with the Google account you enrolled with and every village is open. Use it alongside the System Design track on your dashboard.

Not a student yet? The game is a good way to see how we teach. When you’re ready for live classes, 1:1 mentorship and mock interviews, see the full program.

Questions

FAQ

Is The Lantern Road free?

The first village (Willowmere: scaling from zero to millions of users) is free with a Google sign-in, no card needed. Villages 2 to 29 unlock with a one-time ₹999 payment, or ₹799 through a friend’s invite. Enrolled Prepflix students get the whole road included.

Is a game actually useful for system design interview prep?

Yes, because it makes you practise the decisions instead of rereading them. Each village asks you to apply the concept: trace a request through DNS, load balancers and caches, pick the fix for a failure, estimate capacity, and build the architecture in order. Retries draw fresh questions and bosses mix earlier topics, which is the active, spaced practice that holds up in an interview.

Which system design topics does it cover?

29 topics: scaling basics, back-of-the-envelope estimation, the interview framework, rate limiter, consistent hashing, key-value store, unique ID generator, URL shortener, web crawler, notification system, news feed, chat system, search autocomplete, video platform, cloud file sync, proximity service, nearby friends, maps, message queue, metrics monitoring, ad click aggregation, hotel reservation, email service, S3-like object storage, gaming leaderboard, payment system, digital wallet and stock exchange.

Who made The Lantern Road?

Prepflix, a career accelerator in India for software engineers moving to product companies. The founder, Pranjal Jain, studied at IIT Kanpur and worked as a senior software engineer at Microsoft and at Samsung.

How long does the whole road take?

Most villages take 30–60 minutes: three short lessons, three building battles and a boss. That’s roughly 20–25 hours in total, or under an hour a day across 30 days.

Do I need to know system design already?

No. Village 1 starts with requests, databases and caches, and each building teaches before it tests. If you’ve read the books, the game is a fast way to check what stuck.

What happens if I fail a battle?

Nothing bad. Retry as often as you like. Each retry draws fresh questions, and you need 4 of 5 (or 8 of 10 for a boss) to win. Hints are always available.

When does my 30-day clock start?

At the moment your payment succeeds, not when you sign up. Village 1 is free to play before you decide.

What exactly is the referral?

We refer you for a role you choose at the company you choose, through mentors and alumni in our network who work there. A referral puts your profile in front of the hiring team. It can’t guarantee an interview or an offer. If nobody in our network works at your first choice, you pick another company.

Why is there a verification call?

To make sure the person claiming the refund is the person who played. You’ll explain one design from the game in your own words for about 20 minutes. Nobody’s trying to trick you. Most people find it the most useful part.

Refund or course credit: which should I pick?

Both come with the referral. Take the refund if you’re just here for the game. Take ₹2,000 off the full Prepflix program if you want live classes, 1:1 mentorship and mock interviews next. The credit code is tied to your account.

How do invite discounts work?

Share your invite link from the game. A friend who signs in through it pays ₹200 less. When they pay, you earn ₹200: it comes off your own unlock if you haven’t paid yet, or goes back to your original payment if you have. You can earn up to ₹800.

Can I play on my phone?

Yes. The game works in a phone browser (tap doors to walk), but a laptop is more comfortable for the build-the-system battles.

Challenge terms

The fine print, in plain words

  1. Who can claim. Anyone who paid ₹999 for full access to The Lantern Road with their own Google account. One claim per person and per payment. Enrolled Prepflix students get access at no cost, so there’s nothing to refund. Referral support for enrolled students is part of their program.
  2. The deadline. You must restore all 29 villages, including the final gate, within 30 days (720 hours) of your payment’s timestamp. The time recorded by our server is final. Your deadline is shown in the game.
  3. Verification. After you submit a claim, we schedule a 20-minute video call. You explain one design from the game in your own words. Claims are declined if the account was shared, played by someone else, or automated.
  4. Your reward. After a successful verification, you choose one: (a) a refund of the amount you paid, less any invite rewards already refunded to you, to your original payment method through Razorpay (banks usually take 5–7 working days); or (b) a credit of ₹2,000 off the fee of a Prepflix program, as a code tied to your account. The code has no cash value, can’t be transferred, and is valid for 12 months.
  5. Referral. We refer you for one role at a company you choose, through mentors and alumni in our network who work there. If we have no referrer at that company, you choose another. A referral is not a guarantee of an interview or an offer. You need a current resume or LinkedIn profile.
  6. Invites. An invited friend pays ₹200 less on their first purchase. For each friend who completes a purchase through your link, you earn ₹200, up to ₹800 in total. Rewards come off your own purchase if you haven’t paid yet, or are refunded to your payment if you have. Rewards never exceed the amount you paid. Inviting yourself or creating accounts to collect rewards voids them.
  7. Certificate. Finishing all 29 villages issues a public certificate page with the name you choose in the game (your Google account name until you change it) and your completion date. Anyone with the link can view it.
  8. Access. Your access to the game stays after a refund. If you don’t finish in time, you keep full access. The fee is simply not refunded.
  9. These terms add to the Prepflix refund policy and terms of service. Prepflix may update the challenge for future purchases. Purchases already made keep the terms shown when you paid.
The lanterns are lit

Your companion is waiting at the Citadel.

Play the first village tonight. Decide about the rest after you’ve won your first boss.

▶ Play village 1 free