Red Frog is a beautiful, beautiful beach on Isla Bastimentos. The standard boat tour of Bocas includes a stop at Red Frog (along with Coral Cay and Dolphin Bay), though you can probably arrange for a boat to take you there independently. There is a short hike from where you are dropped off to the other side of the island and the beach. Entrance to the path is roughly $1.
CAUTION: There is a STRONG rip current and swimming can be dangerous.