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Where and what is the highest building in Britain? Not the tallest (that's Canary Wharf Tower in London's Docklands). The highest is the Summit Hotel on the peak of Mount Snowdon (3,560 feet). The flat-roofed concrete building was built in 1936 to designs by Sir Clough Williams- Ellis (creator of Portmeirion, the Italian-style fantasy village on the Cambrian coast). Now, Snowdonia National Park plans to, replace the building with a new pounds 8.5m "visitor centre" to better cope with the needs of the 500,000 visitors who climb the Welsh mountain each year ("climb" is a catch-all word; most people arrive at the top by the Swiss-inspired Snowdon Mountain Railway). Redevelopment hangs, as we have come to expect of virtually every new proposed public building, on funds from the National Lottery.

Lottery funding is also being sought for another building in the wilds of Albion. The "Garden of Eden", intended to fill a disused chalk-pit in Cornwall, is a sci-fi fantasy, a kilometre-long glasshouse replicating, beneath its serpentine roofs, the climate and plant life of rain forest, sub-tropical, desert and Mediterranean landscapes.

The cost of this proposed phantasmagoria is pounds 105m. It is certainly one of the most imaginative and delightful to have emerged from the Lottery scrum. The project, by Tim Smit, landed on the plate of Jonathan Ball, a local architect, who, in all modesty, took it to Nicholas Grimshaw, architect of the much-admired Waterloo International Terminal. Grimshaw and Ball have teamed up with the engineers Ove Arup and partners and Anthony Hunt Associates. The result is a striking design, a bit like some wonderful alien spaceship crash-landed on the Atlantic Coast. Cornwall's traditional industries, like the rain forests, are under threat; the "Garden of Eden" is expected to bring a million extra tourists a year to Britain's "Riviera". They will arrive by car and train; the plants will presumably sail to Cornwall from what remains of the Amazon rain forest on the Gulf Stream; it passes by the proposed site.

A design for a new bridge across the River Thames between St Paul's Cathedral and what will be the new Tate Gallery of Modern Art, has been described as the first in Britain since old London Bridge to include shops, houses and cafes. Aside from Poulteney Bridge, Bath, an 18th-century fancy that does exactly this, here is W Bridges's "plan and elevation for a bridge over the River Avon" at Clifton, Bristol, dating from 1793. The arch was to be 220 feet high. This Georgian delight can be found on one of the handsome postcards sold at the RIBA Bookshop, 66 Portland Place, London W1.