Mineshaft
You're feeling your way through the 1977 Colossal Cave, in REX's twilight. Move the cursor — the light follows. Type a direction (or click a doorway) to move; type LOOK, TAKE lamp, INVENTORY. The drawing on each wall reveals under the light.
Walking skeleton: map, parser, movement, inventory, lamp & darkness, and the magic words are real & faithful. Puzzles/combat/scoring, the Mineshaft text reskin, themed art, and real sound are later phases.