This 5 to 7 hour tour to Tulum and Sak Aktun perfectly combines history and adventure. Leave after breakfast and take a private, air-conditioned vehicle to the ancient port city of Tulum, which you'll explore with an expert historian guide. Then stop for a swim in Sak Aktun ('white cave'), an astonishing underwater cave made of limestone, filled with stalactites. Equipment and entrance fees are included.