We but ours under the bathroom sink. It's not hidden but it's out of the way.
I removed the cabinet doors and raised the floor up to match the door opening.
Now if someone has any ideas to get rid of the odor. I have woke up many times with my eyes already watering, and they were closed! He smells so bad he can't stand it any more and sometimes wakes up the DW so she'll clean it out and get it outside.
I'm trying to figure out a way to rig up a boat bilge blower so it comes on as he steps into the litter box, and doesn't turn off automatically.