The Garden of the Crystal Palace is in the west of Porto and is accessible by bus or if you're good on foot, by very small paths from the river upstream.
Instead of the former Crystal Palace there is a pavilion, called 'Pavilhao Rosa Mota' pavillion. There are mainly sporting events and concerts taking place.
When I was there in September 2011, only a small cafe on the ground floor of the pavilion was opened, a garden is worth visiting. You have a beautiful view over the Douro River and can enjoy a really great evening sunset!