Wellington is at the southernmost point of the North Island (yes, New Zealand has two main islands - the North and the South) and on a harbor that is part of the Cooks Strait. We drove south for an hour from our free campsite and arrived in the city around 9am. We were concerned about finding a place to park the campervan in the city all day, but there is a great parking lot right on the harbor (by the Bluebridge ferry terminal) that allows up to 12 hour parking. (It says it allows 24 hour parking, but we learned the hard way and got a ticket for parking there overnight. Talk to someone before attempting this.)
Before heading to New Zealand, we decided we wanted a hotel in Wellington because we didn't feel super safe camping in a "big" city. Although the hotel was super nice and it was nice to have a real shower and some privacy, it isn't necessary. You can park your campervan for $50 in the campervan site right on the harbor, if you don't want to splurge for a hotel.
Highlights of our day included: walking along the waterfront (saw a penguin, lots of people running and walking, kids jumping from platforms into the, no doubt, freezing cold water, and just generally spectacular views of the harbor), walking up to the Mt. Victoria Lookout (quite the walk but so so so worth it), visiting the Te Papa National Museum of NZ, and dinner at The Tasting Room. In between and all around, there was lots of people watching and checking out the different neighborhoods we had to walk through to get to our next stop.