The Peninsula is a great place if you're interested in arts and crafts, action and sports, lazy days, or tramping, so it appeals to a wide range of people. Mercury Bay is an area with miles of peaceful, beautiful beaches, where you can have a go at deep sea fishing and diving near and around the Mercury Islands, or just simply lay back and watch the world float by.
Whitianga has a cool and lively arts and crafts vibe, and you can have a lesson in bone carving, if that takes your fancy, and there are also plenty of cafes offering local cuisine.
Thames is the peninsula's largest town, with a colorful gold mining history.
Hahei is a good base, with a really good campsite right on the beach, and the walk to Cathedral Cove starts here too. There are plenty of walks over the Coromandel Ranges - the tourist offices will be able to help out with maps and guides. Hotwater Beach is a natural thermal springs area, good for swimming, relaxing, and digging your own hot spring water bath.
Quick Tips:
Be careful on the roads - even though these are the Pacific Coast Highway, some are steep, windy, and narrow, with not a lot of room for overtaking - being patient while stuck behind a caravan or trailer is a must! Also, the roads are often alongside sheer drops over cliffs - don't be too distracted by the breathtaking views - stop at laybys for sightseeing.
Best Way To Get Around:
Car. Definitely. There is a bus service, but it's much easier to have transport of your own, especially if traveling in the summer, as some of the walks are best done early or late in the day. If you're in Hahei, and want to go to Whitianga, there is a ferry service every 15 - 20 minutes from the Ferry Landing just outside Hahei; it saves the very long drive around to it, and only cost NZ per person (you can also take mountain bikes on if you want).