What fascinates about Dungeon Keeper 1 is its engine: it seems very similar to Quake 1, yet it uses sprite NPCs instead of 3D models. The water and lava effects, lighting, and textures feel very Quake-like, yet it has a bit of advantage over the Q1 engine in that the walls are very destructible (like the Voxel environments of Ken Silverman’s Voxlap engine, or another game where everyone loves to mine in the first person). So I wonder: how was this engine created, and how did Bullfrog achieve aspects like destructible walls and the shift from isometric to first person in a late 90s game? Is the engine open source, or is it closed (like many other engines for unique games around that time)?