With in-app purchases included, Alcazar has over 480 puzzles, each a unique Sudoku-like logic problem that involves lines and physical space, rather than numbers.
The rules of Alcazar are simple.
You must cross each tile only once, enter from one door, and exit out another.
With different room sizes, shapes, and barriers, this simple ruleset stretches far across Alcazar's several stages, making for a surprisingly complex logic game.
You can play a demo of Alcazar in a browser.
The full game costs $3.73 USD on Android, but the free version comes with a generous 90 levels, all ad-free.
Grab Alcazar on Google Play.
EDIT: The original article states there are 90 levels available in the free version of Alcazar. This is incorrect. Alcazar (free) comes with 30 levels, and a few free sample levels from each following chapter.