Centennial Park is a pleasant place set in a valley on the edge of Timaru with a creek, a little lake (big pond), some mowed grass, lots of trees and a plethora of trails for walkers and mountain bikers.
This is not really a mountain bike park in that you won't find feature-rich mountain bike trails arranged in a systematic way. There is a kind of random collection of trails that go up and down the valley. They are a few optional steep drop-off features on the south side but most trails are grade three or less when they're dry. There are signs that give trail names but not grade or distance. If you're not a confident rider just stick to the shared use trails. For some grade three or four action the south side is best - although not all that good!
Timaru lacks classy mountain bike trails but it makes up for with a world class jump park at the south entrance to the Centennial Park! It's true - the Timaru Jump Park is just about as good as the Gorge Road Jump Park in Queenstown.
If you like your jumps and lots of air you're going to love the Timaru Jump Park. If you prefer a relaxed ride in a pleasant valley you'll enjoy the rest of Centennial Park but don't expect trails with the technical features found in a modern bike park. It's not that kind of place.