The UCSC Arboretum is home to thousands of plants from all over the world. It is especially noted for its South African collection. The grounds are well laid-out, with intricate pathways bordered by an amazing collection of flowers, bushes, and cacti.
The Circle Trail does not yet have a permanent route across the UCSC campus. The interim route crosses the base of the campus as described in the Complete Trail Description. However, there are many beautiful hiking and cycling trails across meadows and through the redwoods. All are open to the public.
For a full introduction to the Arboretum, check out their website.