Short answers, pulled from the story.
In the late 1980s, the grounds of the Tokyo Imperial Palace spanning 1.15 square kilometers were estimated to be worth more than the entire real estate value of the state of California. This valuation was a concrete reality of the Japanese asset price bubble which inflated land and stock prices to absurd heights between 1986 and 1991.
The Japanese asset price bubble inflated land and stock prices to absurd heights between 1986 and 1991. The bubble collapse was officially declared in early 1992, as land prices dropped the most in this period.
The Plaza Accord of September 1985 led to central banks selling US dollars which caused the yen to appreciate significantly and drop from 238 yen per dollar in 1985 to 165 yen per dollar in 1986. The Bank of Japan slashed the official discount rate from 5.00% to 2.50% between January 1986 and February 1987 to counteract the strong yen but this inadvertently fueled the asset price bubble by making credit cheap and abundant.
The Nikkei 225 index rose from 13,000 in December 1985 to a peak of 38,957.44 on the 29th of December 1989. Stock trading volumes accounted for by corporations rose from 19% to 39% during the 1980s while cross ownership increased from 39% in 1950 to 67%.
It was not until 2018 that Japan's average nationwide land prices finally began to increase year-over-year with a 0.1% rise over 2017 price levels. This marked the first time since the bubble burst that land prices had shown sustained growth.