[@Mae] I'll go with the Tier 1 Secret Tunnel for now. It's more important for Darc to have as many escape routes as he can first before he starts rigging the place to be as deadly as possible for people who walk on two legs or more.

Edit: I should also note that these secrete tunnels would be one that generally speaking, only Darc and other slimes can practically use. Things like ventilation shafts on the ceiling (So they're hard to reach without stacking something to the ceiling) or sewage pipes beneath the floor (Smelly and cramp). Maybe other small sized creatures could get through but for the most part Darc is designing the tunnels for [i]himself[/i] first.