Only the poor are crazy — rich people are “eccentric.” William Cavendish-Scott-Bentinck certainly fit that bill. When he inherited the dukedom of Portland in 1854, he retired to his estate in Nottinghamshire, holed up in the west wing, and had all the other rooms painted pink.

That was just the beginning. Apparently struck with a pathological shyness, the duke had all his doors fitted with letterboxes and would let not even a doctor in. His tenants were instructed not to acknowledge his presence, and only one valet could see him in person.

He wouldn’t go out, but he did go down, employing hundreds of workmen to create a vast underground complex with a library, an observatory, a billiards room and 15 miles of tunnels, one of which was wide enough to accommodate two carriages.

No one knows what he did down there — the ballroom had a hydraulic lift that could carry 20 people, but he never invited anyone to see it. He left the house only at night, preceded by a servant who was ordered to carry a lantern 40 yards ahead of him. He died in 1879, departing a lonely world of his own making.