sentence1: The cave, 54 m (177 ft) long, 15 m (49 ft) high, and 30 m (98 ft) wide, is believed (because of the man-made niches) to have been a nymphaeum, a kind of watery boudoir for the Emperor Tiberius, who retired to Capri in the first century a.d. and built a villa directly above.
sentence2: The cave is 30 m wide and 15 m high.