Nexus > Playground
The Playground is one of the smaller maps. It should be noted that this location is the one seen in the screenshot on the AnsweredPrayers' download page. Upon entering you can see a Phantom (page needed) which you cannot access at first due to the gap between ledges existing there. He's found to the left of the map and will give you the Phantom Prayer once you've spoke to him.
From here, you can access the Underwater Ship from a lift in the house. You can also find the Dark Caves (page needed) from here, where you'll find the Light Prayer .