I read the OP and thought she is exaggerating. 80s decor, well that's subjective and sounds extreme in any case. Signs, not important. Seen plenty of rivers, ponds, cliff drops even!, with absolutely no signs. The claims of 'filth' which is a loaded term made me think, really?
Then I fast-forwarded to the photos. They certainly strengthen some claims. I would say the most outrageous thing is the rotten roof of the swimming pool (not mentioned in OP) followed by the dirty indoor fountain. The 80s decor is not interesting, but the peeling and possibly mouldy wallpaper is. The other criticisms I believe are overblown or non-existent claims. The 'filth' outside was left mid-job, no doubt to be cleared soon. Who knows, perhaps covid has impacted staffing levels and these jobs are not being done as quickly. The gym is overcrowded, sure, as they often are in these places.
OP, I think if you focused on the few most outrageous things you would make a stronger case. Be fair in your criticism. Even if your tripadvisor review stays up, most people will ignore it if it seems overblown. The company could see fit to sue if they thought your criticisms are unfair and defamatory. In fact, there was a case a few years ago. You are publishing your words in the public domain. Sure you can get sued if it can be proved your comments are defamatory.
I really wish people were more aware of this when they leave damming reviews. The business isn't just the owner. It supports many jobs, cleaning, kitchen, laundry, and all those surrounding local businesses that pick up sales. When I read unreasonable reviews, I think of all those people they are slamming with it.