A seemingly no-brainer to me is to have “rare” instances of Cellars spawn during a Helltide, similar to the clickable / destroyable Red Glowing objects throughout the Helltide zones that drop crystals.
You could find multiple treasure goblins inside, a boss, elite pack, treasure chests, etc.
There’s A LOT of room to play around with that small, enclosed, instanced environment.
Use it.
You could even lock them behind a Key that’s dropped during the Helltide, from either the roaming boss or the Helltide chests.