Now, I am on record as hating the term "sandbox", but the idea itself still intrigues me. What would a sandbox setting for H&H be like? Well, I imagine it could be a city-based campaign -- sort of a modern-day version of Citystate of the Invincible Overlord, with a high chance of certain types of encounters on certain streets. So, if you want down this one street like Joe Palooka did, it would be a good place for running into wandering hoodlums.
I've shown pit traps before that combine with flooding traps, but they usually imply some complex plumbing going on behind the scenes to flood the pit. Here we see the au natural option of dumping your foes into a subterranean cavern that floods with tide water. Of course, then the time of day makes a big difference in how dangerous this trap is.
(Scans courtesy of Digital Comic Museum)