I can tell you the path I have taken so far with the keystones.
Talk to everyone around town about the dungeon and find the door lever. The lever is on the wall, past where the mermaid hangs out. You should be able to talk to Cassie about fixing the door. Now go in the dungeon and talk to the mega slime there, you can sex the slime if you want. DO NOT TAKE HER KEYSTONE, if you want a happy slime girl to bang. If you hate the slime and like seeing her cry all the time, then take the keystone, otherwise just leave her be for now.
Head to the Dragon area and talk to the centaur. She should give you a breeding quest for her keystone, when you complete it, use that keystone to open the dragon area.
A Dragon Matriarch blocks the path for the titan area, complete her quest to receive another keystone. DO NOT USE HER KEY ON THE TITAN AREA.
On the left side of the dragon area, you should see a butterfly in the lower field area. Complete her quest and then use both keys that you have to unlock the bee area and the cow fields (pleasure pastures).
In the cow area, find the dryad (near the windmill) and complete her quest for her key. Talk with the Bee queen, then talk to the Dryad about the flowers and she should help complete the quest for the queen. Use those two keys for the Cove (beach area) and the Titan area.
When you pass through the gates for the Cove, there is a new path on your right that leads to the Amorous Hollows (bats area). The Lamia there is stuck, breed the titan she needs and complete the quest. The Orc area has another quest, talk to the Orc Chieftain and complete her quest for another keystone.
ALSO, you can complete the slime quest in the Cove area.
Walk out to the end of the dock, near the Kraken Princess and you will need to swim underwater. The area you need to get to is kind of hard to explain, but standing on the end of the dock, swim out at about ' 2'oclock'. You are looking for a girl in a clam shell who has a perfect pearl that you can give to the mega slime, which makes the slime happy and you can bang her to your heart's content.
With 3 new keys, you can open the Amorous Hollows, the Esoteric Glade, and the Jungle.
When you enter the Hollows there is a spider lady in the very first area (with the stones you can jump across) and she has a quest for another keystone. When you go through the jungle and head towards the harpy area, there is a bunny girl off to the left of the trail with another quest.
The 2 keys you get from the spider and the bunny girl can be used to open the demon area and the harpy area.
I haven't unlocked the last 2 areas yet, still working on the requests, but supposedly Neela (the portal lady) will finally appear and allow you to unlock the portals.