The Winchester Mystery House
Discovery Travel had a show on this before. It was voted one of the scariest historic attraction sites, but in my opinion, it's just very interesting. You can also have tours of the house at night, I think, which will be scarier, but other than that, it's not frightening at all. (And I'm a very paranoid person that gets scared easily.)
It's located near Santana Row and Westfield Valley Fair, which are great places to shop.
http://www.winchestermysteryhouse.com/
Rated on Yelp: 3/5 stars
San Jose Museum of Art
I've never been here, but I think I've heard good reviews of this place before. If you like art, try this place. It's located in Downtown San Jose, near the Fairmont Hotel and some resturants and shops.
http://www.sjmusart.org/
Rated on Yelp: 3.5/5 stars
Peralta Adobe & Fallon House Site
This is a historical site where you can look around... and stuff. I've been here before on an elementary field trip, so I don't exactly remember anything I did here. All I know is that it was fun, but then again, I was in elementary school and if there was no school that day, I must have been having fun. But it does seem interesting. You should check it out.
http://www.historysanjose.org/visiting_hsj/peralta_fallon/
Not rated on Yelp
Almaden Quicksilver County Park
I also came here for an elementary school field trip, and it was fun. :) You can hike, ride horses, or ride a bike here. From the pictures it seems like a very historical and natural site.
http://www.geocities.com/almadenqs/
Rated on Yelp: 4.5/5 stars
Alum Rock Park
"Alum Rock Park, dedicated in 1872, is the first and largest park in San Jose. This 720 acre park features hiking and biking trails, horseback rides, and multitudes of other activities."
I live RIGHT next to it, so if you ever come here, that'd be kinda awesome :D
http://www.sjparks.org/Parks/RegionalParks/arp/index.asp
Rated on Yelp: 4/5 stars
Raging Waters
"Raging Waters in San Jose is the Bay Area's largest water park with more than 30 slides, an interactive water fort and a wave pool. The park is located on the grounds of Lake Cunningham Regional Park just off Tully Road."
I love Raging Waters, but the water always seems too cold and people get injured easily here. There are some fun rides, though, and try sneaking in some food (even though it's hard too)! The food here is expensive!
http://www.rwsplash.com/
Rated on Yelp: 3/5 stars
Tech Museum of Innovation
"The Tech Museum of Innovation in San Jose contains 240 hands-on exhibits designed to show how technology affects every day life. The permanent galleries are Exploration, Innovation, Life Tech, Imagination Playground and The National Medal of Technology and Net Pl@net."
The Tech Museum is pretty fun, because it's hands-on and interesting, but then again, I'm a kid. The most interesting for adults is probably the IMAX movies they offer. (On Yelp they say it's great for adults as well)
http://www.thetech.org/
Rated on Yelp: 3.5/5 stars