Most visitors see Tonga's main island in two parts: first the eastern side and its ancient archaeological sites, and then the western side for its natural spectacles. You can do these on your own via rental car or go with one of the local tour operators. Either way, pick up a copy of the visitors bureau's "The Capital Places Tour," which covers the entire island.
The Eastern Tour
Take Taufa'ahau Road out of Nuku'alofa, making sure to bear left on the paved road. If you want to see tropical birds in captivity, watch for the signs on the right-hand side of the road directing you to the Bird Park and follow the dirt track about 3km (1 3/4 miles). There you will find the Tongan Wildlife Centre (tel. 29-449), which has a fine collection of colorful birds from Tonga and other South Pacific islands. They are kept in cages planted with native vegetation. A star is the Tongan megapode, a native only of Niuafo'ou in the Niuas islands; it buries its eggs in volcanic vents where the temperature is a constant 95°F (35°C), and then flies away, never to see its offspring. Admission is T$3 (US$1.50/75p). The center is open daily 9am to 5pm.
Now backtrack to the main road and turn right toward the airport. Keep left, especially at Malapo (where the road to the airport goes to the right), and follow the Tonga Visitors Bureau's signs, which will show you the way to Mu'a. When the road skirts the lagoon just before the village, watch for the stone-and-brass monument marking Captain Cook's Landing Place. The great British explorer landed and rested under a large banyan tree here when he came ashore in 1777 to meet with Pau, the reigning Tui Tonga. He attended the traditional presentation of first fruits marking the beginning of the harvest season. The banyan tree is long gone.
The next village is Lapaha, seat of the Tui Tonga for 6 centuries, beginning about A.D. 1200. All that remains of the royal compound is a series of langa, or ancient terraced tombs, some of which are visible from the road. A large sign explains how the supreme Polynesian god Tangaloa came down from the sky about A.D. 950 and sired the first Tui Tonga. The last Tui Tonga, who died in 1865, after being deposed by King George I in 1862, is buried in one of the tombs. The 28 tombs around Lapaha and Mu'a are among the most important archaeological sites in Polynesia, but none of them have been excavated. Take the dirt road near the sign to see more of the tombs.
From Lapaha, follow the left fork and the scenic paved road along the coast until reaching the Ha'amonga Trilithon, near the village of Niutoua on the island's northeast point. This huge archway, whose lintel stone is estimated to weigh 35 tons, is 4.75m (16 ft.) high and 5.75m (19 ft.) wide. Tradition says it was built by the 11th Tui Tonga about A.D. 1200, long before the wheel was introduced to Tonga. It serves as the gateway to the royal compound. The present King Taufa'ahau Tupou IV advanced a theory that it was used not only as an entrance but also for measuring the seasons. He found a secret mark on top of the lintel stone and at dawn on June 21, 1967, proved his point. The mark pointed to the exact spot on the horizon from which the sun rose on the shortest day of the year. You can stand under this imposing archway and ponder just how the ancient Tongans got the lintel stone on top of its two supports; it's the same sense of wonderment you feel while looking at Stonehenge in England or contemplating the great long-nosed heads that were carved and somehow erected by those other Polynesians far to the east of Tonga, on Easter Island.
The paved road ends at Niutoua, but a dirt track proceeds down the east coast. Anahulu Beach has a cave with stalactites near the village of Haveluliku. A gorgeous beach begins here and runs to Oholei Beach. 'Eua Island is visible on the horizon.
On the way back to Nuku'alofa you can take a detour to Hufangalupe Beach on the south coast for a look at a natural bridge carved out of coral and limestone by the sea.
The Western Tour
Proceed out of Nuku'alofa on Mateialona Road and follow the Visitors Bureau signs to the Blowholes near the village of Houma on the southwest coast. At high tide the surf pounds under shelves, sending geysers of seawater through holes in the coral. These are the most impressive blowholes in the South Pacific, and on a windy day the coast for miles is shrouded in mist thrown into the air by hundreds of them working at once. Lime sediments have built up circular terraces like rice paddies, around each hole, and the local women come just before dusk to gather clams in the pools formed by the rings. The overlook has benches and a parking area at the end of the road near the blowholes. You'll need shoes with good soles to walk across the sharp edges of the top shelf. This once was an underwater reef, and corals are still very much visible, all of them now more than 15m (49 ft.) above sea level. (Look for what appear to be fossilized brains; they are appropriately named brain corals.) The blowholes are known in Tongan as Mapu'a a Vaea, "the chief's whistle."
From Houma, proceed west toward the village of Kolovai, and watch for the trees with what appears to be black, strange-looking fruit. The sounds you hear and the odors in the air are actually coming from flying foxes, a bat with a foxlike head found on many islands in the Pacific. Nocturnal creatures, they spend their days hanging upside down from the branches of trees like a thousand little Draculas, their wings like black capes pulled tightly around their bodies. They don't feed on blood but on fruit; hence they are known as fruit bats. On some islands they are considered a delicacy. In Tonga, where they live in trees throughout the villages of Kolovai and Ha'avakatolo, they are thought to be sacred, and only members of the royal family can shoot them. Legend says that a Samoan princess gave the first bats to a Tongan navigator.
Near the end of the island is Ha'atafu, site of an offshore reef preserve. The first missionaries to land in Tonga came ashore at the end of the peninsula on the northwest coast, and a sign marks the spot at the end of the road. They obviously got their feet wet -- if they were not "baptized" -- wading across the shallow bank just offshore.
You've now toured Tongatapu from one end to the other. Turn around and head back to town.