Tap an empty square, then pick a height below to build it there. Picking the height a tower already holds clears that square.
Try it above. Every placement counts as a build — the target is one per square. Undo takes back a move, but the build stays on your tab. On Paris and New York, some ringed towers come pre-built and locked.
Every row and column needs each height exactly once. This street has two 2s — can you fix it?
Tap one of the flashing towers, then pick its new height below.
Each edge number is a person at the end of that street, counting the towers they can see — taller towers hide everything shorter behind them.
Finish this street so the watcher sees exactly 2 towers:
Tap any edge number — here or on the real board — to watch it count. On the real board a badge also pops up showing how many ways that street can still be filled. Fewer ways = a good place to think.