What is something fun and fairly inexpensive to do in Seattle?

Two friends of mine are all want to do something fun. We live near Seattle and we want something that wont cost a lot of money. I was thinking the Seattle Aquarium but we need something to do after that too. Any ideas?What is something fun and fairly inexpensive to do in Seattle?
Seattle Aquarium is a nice one. They have a hands-on area where you can actually touch the tide pool animals. After that Pike Place Market would be a great choice. It's right up the steps from the Aquarium, and you can spend as little or as much money as you like. It's a great place to eat, and there are hundreds of shops, vendors, street performers and musicians. Flowers, art, handmade crafts, "flying fish" at the Pike Place Fish Market, and don't forget to check out the "gum wall" downstairs at the Market Theater.
When I was there I went to the Seattle Center. It's probably changed since then. You could take a walk along the piers and check out the food.What is something fun and fairly inexpensive to do in Seattle?
I live in Seattle, and the Seattle Art Musuem is a great place to go, its fairly inexpensive, and its a great place to explore. Lots of fun:) OR PIKE PLACE MARKET its free!:) and its a great ''after activity'' to do! Seattle is very popular for it, it is very close to the water, and so fun to look at all the fruits, and trinkets:)
The ferry to Bainbridge Island. It cost only $6 roundtrip. Go to the observation floor of the Columbia Center, the tallest building in Seattle, for $5. It is a lot higher than the Space Needle and a lot cheaper.