Outdoor winter activities in London could get a whole lot cooler—if a proposal from NBBJ thaws out.

The global firm has released a concept for a series of natural ice rinks, called “Frost Flowers,” intended to float on the River Thames. The plan hearkens back to bygone days when the original London Bridge impeded the river’s flow, causing it to freeze during the winter.

The scheme calls for large circular discs, unfurled from retractable jetties, to be submerged slightly below the surface. By isolating a thin layer of water, the fold-away discs would allow water to naturally freeze, becoming a seasonal public space and creating a central site for the revival of London’s historic frost fair.

Between the 17th and early 19th centuries, during the Little Ice Age, the city sometimes held frost fairs during the winter, on the portion of the River Thames subject to tides where, impeded by the old bridge, it would freeze over. A reimagined annual frost fair might include public ice-skating, markets, and exhibitions, says NBBJ, and would “reconnect London to its heritage.”

In early 2015, the firm proposed a concept for a pair of glass-clad, “no shadow” towers for the river’s banks. Current NBBJ projects under construction include a new hospital in Liverpool, the new Amazon headquarters in Seattle’s Denny Triangle neighborhood, and a stadium for the 2022 Asia Games in Hangzhou, China.