The underground tour looks fun and I'll look into the other suggestions. Really do appreciate it
As for the sort of things we like to do we tend towards museums and sights. Thinking back on our last few trips we've been done bus tours (hop on hop off ones), breweries (just realising we've been to a lot of breweries...), city walking tours, various museums (chocolate, tulip, houseboat, pasta, railway, social history - Anne Frank's House, Eagle's Nest area, James Cook's House, Checkpoint Charlie), general tourist attractions (Alcatraz, Tower of London, salt mines, towers, zoos).
Not particularly a fan of "off the beaten path" stuff, art galleries or anything involving wax works. Military and maritime stuff I'm 50:50 on because it depends on the details.
Ideas for Seattle and New York welcome. New York I think we've come up with Statue of Liberty/Ellis Island (will look into Governor's Island), the Highline (possibly), Empire State Building, Radio City Music Hall tour. Seattle is the Seattle Center for the Space Needle and EMP (if the Lego exhibit stays on), Underground tour, Pike's Place Market.