Check out the table on DMG p.121, Damage Severity By Level. It pertains to traps and hazards.

By way of example, an 11th level party falling into a chasm should take 4d10, 10d10, or 18d10 damage depending on how insta-deathy you want it to be. You say that you want danger, but not too much danger. Coincidentally, that is quite similar to the way this table is labeled (setback, dangerous, deadly). You probably want... dangerous traps and hazards!

NOTE TO NERDS -- Falling damage uses a different damage formula than generic trap/hazard damage; it is not level-balanced but is instead 1d6 for every 10' (not to exceed 20d6). So... maybe that bottomless pit is really just 40' deep but a clever monster cast darkness down there with permanency? Or perhaps there an impromptu landing cushion at the pit's bottom, such as overgrown fungi or even a large-sized plant monster!

Check out the table on DMG p.121, Damage Severity By Level. It pertains to traps and hazards.

By way of example, an 11th level party falling into a chasm should take 4d10, 10d10, or 18d10 damage depending on how insta-deathy you want it to be. You say that you want danger, but not too much danger. Coincidentally, that is quite similar to the way this table is labeled (setback, dangerous, deadly). You probably want... dangerous traps and hazards!

Note that falling damage uses a different damage formula than generic trap/hazard damage; it is not level-balanced but is instead 1d6 for every 10' (not to exceed 20d6). So... maybe that bottomless pit is really just 40' deep but a clever monster cast darkness down there with permanency? Or perhaps there an impromptu landing cushion at the pit's bottom, such as overgrown fungi or even a large-sized plant monster!