The Divinity: Original Sin II Game Guide contains description of all quests available in the game, from the ones connected to the main plotline, up to optional, side adventures. Aside from that, the dedicated chapters contain maps of all locations.
Continue past them to reach the Turtle Beach part of the area where the three turtles will attack you. Kill them before exploring the beach, there is a dig spot hidden along the shoreline closest to the east side, and a locked chest on the west side. With everything you can currently r...