Nimosa and Nymph are in two different pools. To get there, you'll need to go through a lot of Nekos and Kitsunes. You'll need to barter with them, so you'll need to buy a lot of stuff first. The two basic items are the Lolita Cat Hat (available in the Underground Mall) and the Cosmetic Set (available in Upper New Ark). I don't remember the entire list of items you'll need, but each Kitsune or Neko you meet will tell you what they need. Specifically, they'll include a baseball cap, a metal bat, animal pajamas (Mouse and Frog), a gas mask, a penis sleeve, vibrators, a cow top, stinging bug venom, bad fish soup, heart-shaped boxer shorts, a nurse uniform, and a lot of another stuff. You give the item to the Neko, get another item from Neko, and then you can take that item to the Kitsune. This "trading hell" is located on the right and left sides of the main entrance to the temple.
Having reached Nimosa, and then Nymph (or vice versa), you will be able to visit the underground part of the temple and pass the trial of Polkopola.