Basically, I made a saltwater pool out of a glass fishbowl/globe. Here's the photo from Pinterest:
And here's a picture of my crabitat with the pool in the back corner:
I found the fishbowl at a thrift store for like $2, added rocks from the dollar store to the bottom to make it just deep enough for them to submerge, and arranged some moss at the base for them to climb up to the opening. I also added a bubbler and wrapped some artificial greenery around the tube so they can use it to climb in and out of the bowl itself. The bubbler makes the saltwater kinda foamy, but it's doing an AMAZING job keeping the humidity up. Whenever the water gets low, I use a turkey baster to top it off.
I haven't seen my crab use it yet (the other one is molting), but I did catch her checking it out:
She probably would've gone for a dip if a big, scary human wasn't watching
