The geology of the area is of particular interest with many good exposures both inland and along the coast, exhibiting a variety of rock types and structural features such as natural arches, stacks, rock folding and sea caves. A stack of note is Stack Rocks (), two large detached pillars of limestone which in the spring provide valued nesting sites for razorbills and guillemots. In the north, the rocks of , and , together with the extensive moorland on and , give an exposed and mountainous feel to the landscape, cut through by the wooded valleys of the and Nevern. In the west, the National Park is dominated by the broad sweep of St Bride's Bay, bounded at its northern end by Ramsey Island, near St David's peninsula, and at its southern end by Skomer. The southern coast is another contrast, with the limestone plateau and cliffs of the Castlemartin peninsula, the steep-sided wooded valleys inland from Amroth; the Bosherston lakes — now, like much of the coastal strip, in the care of the National Trust — and the tourist resorts of Tenby and Saundersfoot. Between the western and southern areas of the National Park lies the Milford Haven waterway, where the tranquil estuary feeds into one of the finest natural deep water harbours in the world.