[Delphinus]

This is going back some 12 years or so but I had a layover in London for 12 hours, not only that but I had to switch from Heathrow to Gatwick. I took the "tubes" into London downtown, found a locker to store my luggage, and then wandered the sites for a few hours. Westminster Alley, Buckingham Palace, some park (Hyde Park? can't remember) just outside the palace (really pretty) .. watched them building the Millenium Wheel thingymabob ... then serendipitously stumbled across the London Aquarium and well that took care of all the time I needed to pass once I found that little gem. (It was a total "angels singing" moment since I was new the hobby back then and totally binged on anything aquarium related .. oh who am I kidding, I still am that way.) Anyhow it's not far from the old Parliament building, across the river from Big Ben. I'd totally do that if I were you. Anyhow I found I had lots of time to get back to the airport. No worries there. 16 hours, yeah, get a good pair of shoes and walk the sites, that's what I'd do.