Eden Project. Visitors inside the humid tropics biome (dome) at the Eden Project in Cornwall, England. The Eden Project is a horticultural garden centred on two large greenhouses (biomes). The largest, the humid tropics biome, stands 55 metres tall and is over 240 metres long. The slightly smaller warm temperate biome is nearby. Together they form the largest greenhouse in the world. The biomes are geodesic domes holding windows of ethyltetrafluoroethylene (ETFE) plastic. The Eden Project shows the diversity of plant life across the world, and how humans interact with it. It was completed in spring 2001.