The Gedi Ruins, Arabuko Sokoke National Park
Concierge.com's insider take:
The coastal forest of Arabuko Sokoke, north of Mombasa, conceals butterflies, birds, and monkeys in its depths, as well as the ruins of Gedi. This 13th-century Swahili town flourished here for hundreds of years, hidden from Portuguese invaders. The town was eventually deserted, but today, ruined houses, palaces, and mosques are visible amid the trees and tangled vines. Visitors can take a bus, matatu, or car to Arabuko, but there is limited private-vehicle access to the reserve itself, so you are better off going with one of the trekking companies that organize trips from Nairobi or Mombasa.