Palatia Beach is on the uninhabited island of Saria, which is located just above Karpathos. You can get here by boat from Diafani or Pigadia. Multiple boats do trips every week to this island.
The beach is gorgeous with crystal-clear waters and a sandy/pebbled shore. Don't forget your snorkel, it's a great place for that!
Also, you can walk toward the ancient village of Argos, the Syrian pirate ruins (on the top left) and the Byzantine St. Sophia chapel.
When you go for a swim don't forget to search for the cave on the left side. If you've booked a trip with Captain Manolis from Diafani, he'll guide his group there.