what type of building does rainsford encounter on the island he reaches

From the text:

But as he forged along he saw to his great astonishment that all the lights were in one enormous building--a lofty structure with pointed towers plunging upward into the gloom. His eyes made out the shadowy outlines of a palatial chateau; it was set on a high bluff, and on three sides of it cliffs dived down to where the sea licked greedy lips in the shadows.