High above Dartmoor stands a windswept and spectacular country home that looks as ancient as the landscape it's set in: Castle Drogo. But this remarkable building was only constructed 100 years ago, the last castle ever built in Britain. Today, this landmark building is under serious threat. In their biggest current project, costing £11m, the National Trust is restoring the castle, replacing almost the entire roof before the building rots to pieces. Time Team has exclusive behind-the-scenes access to the hugely ambitious restoration project.