I first read about the Thames in London freezing over a few years ago, and it really caught my imagination. Between 1309 and 1814 (during the Little Ice Age), the Thames froze at least 23 times, and on five of these occasions the ice was thick enough to hold a "frost fair." Tents and booths were set up on the ice with food (roast ox), drink (gin), and games (bull baiting and fox hunting). Some tents contained brothels. At the last frost fair, in 1814, an Elephant was led across the ice at Blackfriars Bridge. The Thames has not frozen solid since.
Slate just ran a piece on the printers who set up printing presses on the ice and churned out engraved and letter-pressed sheets of paper as souvenirs. These souvenirs contained verses and engravings of the festivities.