For a bit of heavy hiking, catch a Mulivai, Salani, Sapunaoa, Siumu, or Vaovai bus up the Cross Island Highway to a turnoff on the right for Lake Lanoto'o, otherwise known as "Goldfish Lake," high in the center of Upolu at 590 meters above sea level. Walk straight west on the access road for just under an hour until the road ends. From here a sign should point the way west to the lake, another one-hour climb. When you arrive at a destroyed microwave reflector on top of a hill, the lake is just below you to the left.
The poorly marked way takes a bit of intuition to find but some of the locals living on the main road to the trail can act as guides (S$20). There's no admission fee to the lake, and if you take your time and are good at finding your own way, you'll be okay. The route to the lake is muddy following heavy rains, so only go after a couple of days of sunny weather. Expect fallen trees across the route and some confusion at the beginning. This is a very strenuous hike, so be prepared. In 2003, Lake Lanoto'o was declared Samoa's second national park, so the trails and signposting should improve.
The opaque green waters of this seldom-visited crater lake are surrounded by mossy green bush dripping from the mist. Swimming in the lake is an eerie experience. To add to the otherworldliness of the place, Lake Lanoto'o contains goldfish, but you'll have to wait patiently if you want to see any from shore (bring along bread to feed to them). This hike is ideal for seeing Upolu's high-altitude vegetation without going too far from town, but sturdy shoes, long pants, and water are essential.
On your way back to Apia stop to visit the Baha'i House of Worship (1984), Mother Temple to all Baha'is in the region. The temple is at Tiapapata, eight km from Apia and a 30-minute walk down the highway from the Lanoto'o turnoff. The monumental dome soars 30 meters above the surrounding area and has nine sides, symbolizing the unity of the nine major religions of the world. Inside, the latticework of ribs forms a nine-pointed star at the apex of the dome. The seating is arranged facing the Holy Land (Israel) because this is the final resting place of Baha s' Ullah (1817-1892), Prophet-Founder of the Baha'i Faith. This majestic building, funded by Baha'is around the world, is open to all for prayer and meditation daily 0600-1800. Also visit the information center, to the left as you approach the temple. Samoa's first head of state, His Highness Malietoa Tanumafili II, was a Baha'i. The Vaoala bus comes to within a 30-minute walk of the temple.