First, hit up the Weta Cave.
This "mini-museum" features props and displayes from your favorite WETA films, and has WETA merchandise available for purchase.
If you want to take a tour of some of the sites where Lord of the Rings was filmed, try Wellington Movie Tours. They have several different tours (full day or half day) that include lunch, and depending on which you choose, you can see up to 25 LOTR sites near Wellington, including a "Bush walk to Rivendell."
But don't limit yourself just to LOTR activities, check out the sites and the nightlife. Here are a few of Guillermo's favorite places to go:
Logan Brown ("FANTASTIC", says G)
To find more things to do in Wellington, click here.
I've never been to Wellington - this is just a helpful guide to some cool things that have been highly recommended. Please feel free to post your recommendations below for others to read!