Its hard to miss Sphinx's Pyramid on world map, so i hope you know where it is. Pyramid has three floors. You can visit F1 whenever you want, but passing through door on F2 require a key you can get from DesertP. Talk to her for few times until Moon Festival event step. SphynxP will interfere DesertP dance.

Offer your help.

Next morning talk to DesertP again, get a key and go to Pyramid. Now you can pass through door and access F3. There will be unconscious SphynxP near stairs, so you'll have to ask one of companions to look after her while you beat CrusaderP.

If you had Cinder Ribbon (avaliable during said Festival at MerchantP, or at any other Moon Festival) and gave it to DesertP, and took her with you to F3, there will be few fun dialogue lines between her and CrusaderP.

After few day visit SphinxP at Pyramind F3, and she will ask if you want to explore Sphinx's Fortress.

Here will be some brawling, so not recommending for weak knights. You can cheat a little to pass through Fortress, but we're going for Moss Princess, right? So you can't avoid fighting sand snake hidden boss. You will need a mace, but there will be nice one in reward chest after beating sand snake. KoboldP will be helpful af.

Maze part of Fortress is easy. Just hit crystals, read signs, step on buttons, avoid boulders etc.
Only tips i can give you here without making it too easy are:
- Use Shift to run through corridor with rolling boulder;
- Use KoboldP to jump over floor hole with moving cyrcle;
- To defeat mummy, use torch near entrance at mummy's room.

Save Crystall room is crossroad. To the right is boss fight room. Quite easy, but if you're in hurry, you can use KoboldP to overjump Sphynx statue. Easy win with no achievement.

To the left from Save Crystall is secret passage, starting where skeleton is. Sooner or later, you'll get yourself in secret room. Secret boss is easy, but spawn unlimited snakes with no rewards. After beating sand worm. you will get chests with stuff and Lamia Egg. Go downstairs to find Lamia Princess and her subordinates.

Destroy rocks with mace, see a cutscene, return to Save Crystall room and clear dungeon. Or dont. You can exit the way lamias used and go outside. However, loot is loot.

With that, Sphinx's Fortress is finished. You can repeat is every few days or so by talking with SphinxP, but its always same and no point to replay. Secret boss wont respawn.

Now its time to visit Oasis at east from Desert Reign, when freed lamias cleared the way to Lamia Sanctuary. Necessary equipment for this part is Fish Lungs you can purchace from Mouse Tinkerer after dontaing 10 Cogs (loot from Ancient Battlefield location accessed via Golem Reign).

At northern part of Sanctuary you will see path downstairs with six torches. Simple "meet a pair" game, but you should save here since reset is broken. Solution is top left with middle right, middle left with lower right, lower left with upper right

Once you're done, Sunken Temple entrance will appear.

I dont want it too easy, so just say there's a switch in dark room used to open F2 door. To go there you will need Fish Lungs. Of course, you can overjump water border with KoboldP, but game wont let you go to next level. Not tried to use water-breathing progency tho. F2 and F3 are easy, only one iq10 riddle with fountains and one golem.

Once you're done with Temple, exit to Lamia Shrine. And go back to Sunken Temple F3. At room where you defeated golem you'll find Moss Princess to join you.

Achievement and MossP herself.

Moss Princess count as Progency and will follow you in NG+ without losing any stats or equipment. Her special ability is stealth mode similar to Slime Princess, but in reverse. MossP is hidden by default and become visible while using Ctrl.

She can help you to sneak past guards (replace Sleeping Powder) and is invisible for enemies. Only weak point is bumping into sleeping sisters of MouseP will wake them up as usual.