Which cruise line? Ships leave from Pier 91 and Pier 66. Norwegian Cruise Line and Celebrity Cruises depart from the Bell Street Pier Cruise Terminal at Pier 66. Holland America Line, Princess Cruises, Carnival and Royal Caribbean will depart from the new Smith Cove Cruise Terminal at Pier 91.
My dd and I stayed almost right across the street from Pier 66 at the Marriott Waterfront. We weren't going on a cruise, but we loved the location. Very easy to walk a lot of places. If you are taking one of the cruise lines that leaves from Pier 66 you could pretty much walk from the hotel there.
http://www.marriott.com/hotels/travel/seawf-seattle-marriott-waterfront/