Caving, both on land and underwater, is spectacular and easily accessible. Tongatapu has one cave, Vava'u has several and 'Eua has dozens of limestone caves. Exploring underwater caves is best on Ha'apai, which has a deep cave full of flashlight fish. With water temperatures around a pleasant 23°C to 30°C (73°F to 86°F) snorkelling, surfing, swimming and diving are great in any of the major island groups. Volcanoes, shipwrecks, canyons, coral reefs, a stunning variety of reef fish and visibility that in places reaches 70m (230ft) make the snorkelling and diving spectacular, and the surfing is as good at any time of year as it gets anywhere in the world. The surf's best on Ha'apai and Vava'u, and the best surfing on Tongatapu is at Ha'atafu Beach.

Kayaking is increasing in popularity, and Tonga offers a wide scope for challenging sea kayaking. The Vava'u group offers clear, calm and sheltered waters, and the Ha'apai group has a little more open sea. The whale-watching season is from June to November on Tongatapu and Ha'apai, and July to November on Vava'u. On trips to watch whales, underwater microphones catch whale songs for you to hear. Game-fishing charters are showing up all over Tonga, and you can also indulge in the less competitive form with a good book, a deserted beach and a long line.

On 4 July Tongans celebrate King Taufa'ahau Tupou IV's birthday with the Heilala Festival, which becomes a week-long bash featuring parades and processions, music festivals and competitions. It coincides with the flowering of the heilala, Tonga's national flower. The torch-lighting ceremony, Tupakapakanava, coincides with this festival. People carrying flaming torches of dry reeds line the northern coastline of Tongatapu, and the Tongans liken the festival to Guy Fawkes Day in the UK or the USA's 4 July fireworks. On Vava'u, the Crown Prince's birthday in early May kicks off a week of partying with the Vava'u Festival. Also in May is the week-long Red Cross Festival, which is followed by the Red Cross Grand Ball.

In early June the Ha'apai group celebrates the three-day Ha'apai Festival, coinciding with Emancipation Day festivities. In a nation as Christian as Tonga, locals take Easter seriously, and celebrate an Easter Festival, with youth choirs, passion plays, concerts and cultural performances. All the major island groups host agricultural fairs from late August to October, and they are presided over by the king. Late September sees the Tonga International Billfish Tournament celebrated, attracting local and international anglers to Vava'u. Another international competition is the Miss Galaxy Pageant in Nuku'alofa. The contestants are all men, or fakaleiti, the local version of transvestites.