Napier's main attraction is its Art Deco architecture, and you can explore it on your own or with a guided walk from the Art Deco Centre on Tennyson Street. The self-guided walk takes about ninety minutes and covers the key buildings along Emerson Street, Dalton Street, and Tennyson Street. The guided tours add context about the 1931 earthquake and the rebuilding effort that is hard to get from a pamphlet.
Beyond the architecture, the National Aquarium of New Zealand on Marine Parade is genuinely good -- small but well designed, with a walk-through oceanarium tunnel and a kiwi enclosure. Cape Kidnappers gannet colony is a must if you are here between November and February, when thousands of birds nest on the dramatic cliff edges. The trip out there, whether by tractor along the beach or on foot, is an experience in itself.
The Hawke's Bay wine region surrounds Napier, and a day visiting cellar doors is one of the best things you can do. Standouts include Craggy Range, Te Mata Estate, and Church Road -- the oldest winery in New Zealand. Many of the vineyards are close enough to reach by bicycle, and several operators rent bikes and provide maps for self-guided wine tours.