... like assassinate the NPC they were hired to protect for no other reason than because they could.

Welcome to the fold, that is the exact reason why DMing is one of the most rewarding things you can do with friends. We just had an extended session at my place yesterday given we were all off work at the same time for once (yay holidays)!

If you look at the last picture you can see that it’s highly modular with pieces maybe 1.5’x1.5’ or so.