Lots of mermaid fiction! (Most mermaid science fiction assumes that other sapient life is also aquatic, but there are several that posit sapient flying aliens; terrestrial aliens ever show up but not often and mostly the authors don't seem to have thought through the implications of not being able to casually move in three dimensions.) Lots of mermaid Discourse! (About as much of it as on Amenta has to do with reproduction, but in different ways; other topics of dissent include people calling each other apologists for one side or the other of the Southshallowshelf War, discussion of ethical consumption habits, whether or not Akeekikekao did anything wrong, and sensitivity towards the disabled) Lots of mermaid science and engineering! (Their transportation is fairly abysmal) Lots of mermaid history! (Metallurgy universally started in the Deepdowns and worked its way up! The K'k'k'aouiiiia'keka Empire had a system of executing native citizens cleanly and sentencing people in conquered territories more harshly than necessary to compensate for the lack of native condemned criminals for cleanup and thus is generally considered to have been an unusually horrible polity even for an empire!)

Meanwhile, the Amentans have been thinking about how to let mermaids visit Amenta! Amenta does have an ocean but they don't know if it has all the things mermaids need to be comfortable. The suits don't look suitable for long term use, although a mermaid in a suit could maybe be in a wheelchair (a reclining one, if they don't bend that way) and toted around? For the day-and-a-half trip to Amenta maybe they could be in an aquarium tank? There are some large ones and they can be put on wheels, though they acknowledge it would not be the most stylish accommodation.

The mermaids have been working on the suits too--even if Amentans are going to come underwater mostly it still seems like a good idea. Mermaid tails are extremely flexible and the wheelchair idea should probably work, although it would be more comfortable if there were a pool or aquarium or something to retire to when not actively going around places. 

Okay! They can bring over a few big aquarium tanks of the kind you'd keep a large octopus in; it will be less roomy for the mermaid than the hypothetical octopus but it will fit through doors and stuff. And they can empty a big swimming pool and put mermaid-approved water in it for in between touristing.

Also, they have scuba gear and people who know how to use it now!

The mermaids will delightedly escort scuba amentans to the city, where chambers have been prepared drained of water and with amentan-appropriate furnishings! Some mermaids (who have been carefully vetted by the government, just in case) would love to visit Amenta!

The mermaids' tanks are rolled into the ocean to fill with presumably ideal local water and a mermaid apiece, and then they and their suits and any other luggage are rolled aboard a starship and brought to Amenta!

Scubamentans appreciate the air rooms (though they do want to make sure they're ventilated properly).

They're not ventilated directly to the surface but they do have machines doing gas exchange to make sure the air is an appropriate chemical mix that doesn't fill up on carbon dioxide and suffocate anyone.

Oh good! Then the Amentans will be quite comfortable in there between oxygen tanks, and go swimming around the mercity, taking tons of pictures with underwater cameras (plastic bags not being rated for this pressure).

This mermaid city is especially photogenic, having been built half-into a live coral reef. Mermaid architecture (at least as indicated by this particular city) is built into surfaces as much as on them. Plenty of things have walls for privacy, but within buildings or rooms things aren't really organized with a concept of "down" in mind. 

Curious mermaids are plenty attracted to the exotic, alien Amentans, although most watch from a polite distance. 

Most of the exceptions are small children too young to know any better. 

The Amentans love the little merbabies and will pet any merbabies who swim up to them and let them stick to the wetsuits if they can.

Merbabies can totally stick to the wetsuits. Merbabies are delighted to stick to the aliens and their wetsuits. 

Older mersmols have SO MANY QUESTIONS ABOUT SPACE.

The Amentans can answer space questions!!!!

Adult mermaids come collect their children from the Amentans when one or the other party leaves the place where they are, but are otherwise mostly content to keep an eye on their children and otherwise let them free-range. 

There are individuals and couples who don't obviously have any children, but nobody at all has exactly one. 

That seems reasonable to the Amentans.

They'd like to see museums! Are there those?

There definitely are those! This is a museum of art and this is a museum of science and this is a museum of history, which one do they want to do first? 

They'll split up!

Okay!

Mermaids don't really have paintings--that doesn't work very well as a medium underwater. But they have mosaics and carvings and statues and tapestries. 

The Amentans take pictures of it all and ask about the tropes represented.

This trope is Pre-Creche Mother Swims Away From The Babies She Didn't Choose, Crying and is a popular go-to if you want to make your audience cry. This trope is The Abomination and can be quality horror or cheap shock value depending on how it's used; these are all "quality horror" ones. This trope is seaweed in undulous shapes meant to evoke the form of mermaids having sex and is frequently used in borderline-erotic romance art. This trope is a heroic mermaid, either lethally wounded or fatally poisoned, swimming away from their loved ones to die alone because they're cut off from civilization and there aren't any corpse collectors. 

The Amentans are super into all this. What's the deal with the Abomination?

The Abomination was bad and evil and wrong. It was a fish. A predatory fish. That ate merbabies. It was bad bad bad. It's extinct now, thankfully. It was so bad though. 

Gosh! There used to be some things that ate Amentans but never as a primary food source. Most of them are extinct but they didn't actually do that on purpose except for a couple kinds, they just crowded most of them out with development. Some are still alive in the tropics or Arctic where few Amentans live and people have to watch out for them if they are there for some reason.

Well, Amentans were lucky enough never to have a period of development when they had to leave most of their babies to death by exposure or predation. That would change the ecological math a lot. 

Mermaids aren't in the habit of driving things extinct, and have in fact gone out of their way to avoid it when possible! It still happens, sometimes, but they've found it a sound policy overall. Why don't many Amentans live in the tropics?

Amentans don't season in the tropics, or the arctic! They get stuck in spring (the fertile season) and that gets really annoying after a while, especially if you don't have a credit.

Do they not have reliable birth control?