Thanks :) It's my own engine, but makes use of libGDX to help with some low-level rendering since plain OpenGL is a bit too raw for my taste. It's hacked open so I can use my own game loops and own everything else.
Maps are mostly randomly generated, so they're almost entirely just code. The small chunks which are static I define inline as a 2d array of chars, like the roguelikes of yore.
I do a loads of my own artwork, but for the most part it's modifying, re-coloring and extending existing tilesets. It's much easier to follow a consistent design language than invent your own. This game is mostly based brilliant work from https://pita.itch.io/, and http://www.squidi.net/pixel/char.default.php