Belly button glory holes are genuinely such an enormous fantasy of mine, both giving and receiving.
Like just imagine lotsss of navel-sensitive people have just gathered and are randomly paired up, and each have a turn at putting their belly button up against the hole and the other can do what they want to it, and there's tools provided and fuuuuuck. You could also sign up based on what you want and be paired up that way, like some people might only wanna be licked/pleasured while others would wanna be tortured etc. As a navel switch it's my actual dream ahaha just imagine both being able to put your belly button up into an opening and have a stranger just get you off, and then be presented by their belly button and then have the chance to get THEM off
Personally i'd like to start by licking them gently to gauge how sensitive they are overall, and then use something like a toothpick to probe around their belly button to find all their most sensitive spots. I'd have a notepad with me to sketch it out almost like a map, and then i'd really hyperfocus on those spots while reassuring and praising them gently, then sometimes switching back to licking if they really enjoyed that, experimenting with pressure and patterns.