While this isn't close enough to "spelunking" but here's a list of some of the major Endchan boards.
>>>/ausneets/ - See here: >>23435 - unnas, wanking and Priscilla spam.
>>>/qanonresearch/ - Anons researching qanon, worship Trump and baking their breads. Oh Baker is the BO, as I realized later. Most of them moved back to 8coom finally this *oomer meme is god for something.
>>>/bbg/ - Bonbibonkers. Fanboys of a teenage tiktok grill with heavy makup, wigs and weird heda. They fled from the tyranny of 4chan mods.
>>>/yuri/ - Fat neckbeards posting cute lesbo anime grills. I think. It's a chill board.
>>>/pol/ - Promoting Hitler and German national-socialism, appropriating just about any civilizational achievement. 8/pol is banned there.
>>>/b/ - Repository of altchan spam.
>>>/AM/ - Anime, not /am/.
>>>/rapport/ - Female celebrity pics, short discussions
>>>/hydrus/ - Anonymous (media) file organization and sharing service.
>>>/news/ - It's tha /pol/ news.
>>>/operate/ - Complaints and suggestions ignored.
>>>/rus/ - is getting resurrected. Russian random. Other Russian boards exists like >>>/ca/ or >>>/ruspol/, and others. Most users left due to 500 errors, then the bunker times.
>>>/euzn/ - Fresh board for hapas. And any other Eurasians.
>>>/os/ - Online security. I really should browse this. And probably most of us.
>>>/tech/ - This one too.
>>>/v/, >>>/tv/, >>>/mu/ >>>/int/ - Mandatory, but almost no users.