Note to readers: Palau government charges $100 US per-person just for the permit that allows you into Jellyfish Lake. You will also pay anywhere from $90-135 for a tour group to take you here. Ante up and do it. We booked through Impac tours for $90/person, which was the cheapest we could find. They did a fantastic job. They picked us up from our hotel free of charge. The tour lasted 6 1/2 hours and included a trip to Milky Way, two snorkeling stops, lunch, and Jellyfish Lake.
Jellyfish Lake is unlike anything you will ever experience. It is a steep but short hike to the lake, maybe 10 minutes. The lake is chock full of amazing, non-venomous Jellies. You literally float in a sea of these amazing creatures in all sizes. A must-do in Palau, regardless of the cost.