one of my favorite ways to spend a leisurely day with out-of-towners is to take a morning to ferry to bainbridge, then walk from the ferry dock to cafe nola on winslow way for brunch. wander back to the ferry dock and return to seattle. once off of the ferry in seattle, wander north along the touristy waterfront/pier area and visit the olympic sculpture garden. from there, you're close enough to walk to seattle center (where the science center, space needle and emp are located). or, just turn south and wander through belltown to pike place market. making sure to stop for random coffee and snacks as things catch your eye.
other than whatever you choose to spend on food, this is a fairly inexpensive way to spend a fun day. you only pay for the ferry one way, and the sculpture park is free...as is window shopping, people mocking and picture taking.
2009 BMC Road Racer SL 01 / Specialized Ruby 155
2007 LeMond Reno / Luna Chix Team Saddle
1980-something Lotus Odyssey / Brooks Finesse
1992 Bridgestone RB-2 / Brooks B-17 Imperial
Nada Bike singlespeed / Brooks Team Pro in white