I Built “Serendipity Trip” — Throw a Dart on the Map for a Truly Random Journey

Lead
Overview
The concept — a trip that welcomes chance
Truly random — computed fresh every time
Set your area by prefecture — for real trips too
Features in the initial release
Screen flow
Download
What I learned building it
Summary
Notes

Lead

Hi, I’m Pomarano.

This post is in the Daily category — about a travel app I built and released.

“Serendipity Trip” (偶然の旅 in Japanese) is on the App Store and Google Play.

The concept is simple: throw a dart at the map and let it pick your destination. When you don’t over-plan, unexpected scenery and encounters can show up along the way. That’s the kind of serendipity this app is for.

This post covers why I built it, how the randomness works, and what’s in the initial release.

Japanese version of this post: here

Overview

flowchart LR
  A1["Concept<br/>Serendipity Trip"]
  A2["Random pick<br/>Computed each time"]
  A3["Serendipity Trip<br/>Initial release"]
  A4["Store launch<br/>iOS / Android"]

  A1 --> A2 --> A3 --> A4

  classDef concept fill:#e8f4fc,stroke:#3d7ea6,stroke-width:2px,color:#1a1a1a
  classDef app fill:#e8f5e9,stroke:#2e7d32,stroke-width:2px,color:#1a1a1a
  classDef meta fill:#eceff1,stroke:#607d8b,stroke-width:2px,color:#1a1a1a
  class A1 concept
  class A2 concept
  class A3 app
  class A4 meta

The concept — a trip that welcomes chance

When you plan a trip, do you ever get stuck on “where should I go?” You list options, compare them, and end up back at the usual choices.

Serendipity Trip is an app that leaves the decision to chance.

Idea	What it means
Random destination	Where the dart lands is today’s destination
Welcome the unexpected	Unplanned places can bring new views and encounters
Keep a record	Log prefectures you’ve visited on a color-coded map

Think of throwing a dart at a map. Swipe up on the map and the dart flies; where it lands becomes your destination. It works for a weekend with no plan in mind, or a short trip when you want a change of pace.

Truly random — computed fresh every time

Some “random” apps just pick from a fixed list. Serendipity Trip calculates a new point every time you swipe.

Roughly:

Pick one prefecture at random from the ones you’ve selected (Japan has 47 prefectures)
Find a random point inside that prefecture’s boundary
Drop a pin and show the prefecture, municipality, and coordinates

There’s no pre-made list of “100 destinations.” Each swipe starts from scratch, so the same spot won’t repeat in a mechanical loop.

Not sure it’s random enough? Swipe again as many times as you like.

Set your area by prefecture — for real trips too

You can limit random picks by prefecture.

Setting	Example use
All 47 prefectures	Full random — you don’t know where you’ll land
Kanto only, Kyushu only, etc.	Pick a broad region, then let the dart choose
Prefectures you haven’t visited	Shortcut to target only unvisited areas

“I want to travel in Tohoku this holiday, but I don’t want to pick the prefecture myself” — narrow the area, then throw the dart. You can use it to decide where to go on your next trip.

Features in the initial release

The app includes:

4-1. Random — decide with a dart

On the Random tab, swipe up on the map → the dart flies and your destination is set
A pin marks the spot. Shows prefecture, municipality, and coordinates
Copy coordinates or address with one tap
Past results stay in history (with date/time; tap to show on the map again)

4-2. Area settings

Select multiple prefectures as random targets
Shortcuts: add all “not visited” or “passed through” prefectures, select all / clear all

4-3. Experience — log where you’ve been

A color-coded map of Japan shows visit status by prefecture.

Status	Example meaning
Lived	Stayed for a long time
Stayed overnight	Traveled and slept there
Walked	Explored on foot
Passed through	Train or car transit
Not visited	Haven’t been yet

Register by prefecture and add notes. If you have multiple entries for the same prefecture, the deeper experience wins on the map color.

4-4. Registration history

List of logged places
Filter by prefecture, view details, delete

4-5. Other

First-run tutorial (Random → Experience → History)
Current location, button to reset map north
Records saved on your device (no account required)

Screen flow

Blue = random experience · Gray = logs and settings

flowchart TB
  H["Home (3 tabs)"]
  R["Random<br/>Swipe for dart"]
  E["Experience<br/>Japan map log"]
  L["Registration history"]
  A["Area settings<br/>Pick prefectures"]

  H --> R
  H --> E
  H --> L
  R --> A
  R -->|"After you go"| E

  classDef random fill:#e3f2fd,stroke:#1565c0,stroke-width:2px,color:#1a1a1a
  classDef record fill:#e8f5e9,stroke:#2e7d32,stroke-width:2px,color:#1a1a1a
  classDef nav fill:#eceff1,stroke:#607d8b,stroke-width:2px,color:#1a1a1a
  class R random
  class E record
  class H nav
  class L nav
  class A nav

Typical flow:

In area settings, limit to prefectures you haven’t visited
Swipe on the Random tab → destination decided
After you go, register the prefecture on the Experience tab
Next trip: target unvisited areas only and throw the dart again

Download

Store	Link
App Store (iOS)	Serendipity Trip
Google Play (Android)	Serendipity Trip

The app UI is in Japanese for now. Random history and visit logs are stored on your device.

Screen	Store messaging
Random	Dart picks destination · swipe gesture
Experience	Color-coded prefecture map
Registration history	List of visits
Area settings	Filter by prefecture

What I learned building it

What worked

The dart metaphor made “random” easy to grasp
Prefecture-level area settings support “I choose the region, chance chooses the detail”
Linking the experience map with random settings (one-tap unvisited prefectures) helps motivation to travel

Still figuring out

Random results and visit logs are separate — you register visits on Experience manually after a trip
On islands or narrow regions, calculation can occasionally take a moment

What I’d like to add later

One-tap registration from a random result to Experience
English UI in the app
Export visit records

Summary

Serendipity Trip picks your destination with a dart and helps you enjoy chance encounters along the way
Destinations are computed fresh each swipe — truly random
Prefecture-level area filters work for weekend trips and hunting for places you haven’t been
Available on the App Store and Google Play

If you’re stuck on where to go, try throwing the dart once. I’d love to hear how it goes in a comment or on X.

Notes

The app uses location features. Check your device settings when you use it.
Ads are shown (banner, and occasional full-screen ads tied to dart throws).