Location: Surrey, England
Price: approx. $284,657,826
Square footage: N/A
At the turn of the 20th century, James Whitaker Wright, a corporate swindler whose misdeeds caused a panic in London, committed suicide immediately after being convicted of fraud. In better days, he built himself a country estate on about 1,400 acres now known as Witley Park.
Wright spent nearly $285 million in today's dollars on the land and the mansion. That's without taking into account the landscaping, which reportedly cost the staggering equivalent of $84,862,552 in present-day terms. He leveled hills that blocked his views, built a wall around the estate, and created three artificial lakes. Under one of those lakes: this glass-domed billiards room, accessed by tunnel. The mansion is long gone, but the fantastical submerged room remains, abandoned and locked up today.