I will soon be going on a trip with my partner to Japan, and we're curious if there is anything wam-related we should try and do when in Japan. Does anyone have any recommendations, whether in a love hotel or elsewhere? Any suggestions at all would be appreciated!

More on the wet side than the messy side, but https://www.youtube.com/watch?v=uD2cGWdPyG4 is a SFW video of a love hotel room that has not just its own pool but also its own, fractionally unsafe-looking, water slide. You could splash out for a stay there, ho ho. (And there's nothing stopping you from taking a slide while clothed, if you like.) I've seen passing reference to it not being the only one, but cannot prove this.

Slightly more messily, the room also includes what they refer to as a bath mattress. To me it looks like the sort of thing you might have a nuru massage on. I don't know whether they sell the nuru gel there but it seems likely. It's more lube-y than messy but, y'know, close enough.

https://how-to-sexfriends.com/messyplay/

We used a love hotel and found a Massuse willing to do messy play but she brought all the plastic bags to clean up and we spent some time cleaning up the tub and she brought sheet to cover the bed with

At Tokyo Buggy Village, you can ride ATV's through the mud and get super muddy.

However, if you don't want to ride an atv, you can also pay just to access the mud course and play in the mud.

For additional pay, they will even dump mud over your head with a digger.

Their website is cimax.jp and there is a Japanese fetish site called Soakedwoman that films their mud scenes there.

I don't know about Wam, but if you can afford the splurge and go to Morimoto's "Atelier Morimoto XEX" you will find one of the best restaurant experiences of your life!