The southern coastal road (Route 4) strings together several of Guam's most historically and scenically interesting spots, all within easy driving distance of Cetti Bay.
Umatac is the closest village to the south, about 5 km along the coast. It is where Ferdinand Magellan is said to have made his first landfall in the Marianas in 1521, and the village commemorates this with a fort and an annual festival. The bay at Umatac is calm and picturesque, and there are remnants of Spanish-era defences on the hillside above. It takes about 20 minutes to poke around.
Merizo lies a few kilometres beyond Umatac and is one of the best-preserved Chamorro villages on Guam. From Merizo, short boat trips run out to Cocos Island — a small reef-ringed island with good snorkelling and a calm, shallow lagoon. Cocos Island is one of the few places in the Guam area where you can actually swim in clear water without strong currents.
Inarajan on the southeastern coast, reached by continuing on Route 4 or cutting across the island, has a natural swimming pool formed by a reef — popular with families and one of the better swimming spots on the southern coast.
The full loop around southern Guam on Route 4 takes about three hours without stopping; allow a full day if you want to stop at Umatac, Merizo, and Inarajan.