Hiking in Leona Heights Park!There are lots of great places to go hiking in Oakland. Many of them are highly accessible (including paved walks and short, easy walks) but there are also longer, more strenuous hikes.
http://www.bahiker.com/eastbay.html is a very thorough East Bay hiking source. http://www.ebparks.org/activities/hiking is the East Bay Regional Park District guide to hikes - lots of detailed maps and details.
When hiking, some things you might see include trees (including redwoods!), animals, mushrooms, and more.
See also: walking, bicycling.
Here are some great places to go hiking: