For those born without a sense of humour, Halopedia has an article on High Charity.
 High Charity is a lost space mushroom floating in a vacuum, powered by a Forerunner hamster on a spinning wheel. A civil war broke out through High Charity because The Prophet of Truth thought the Elites weren't gangster enough so the Brutes took their place and started shooting the whole place up. A Pelican who ate a pet fish of Graveminds crash landed and infected it with the Aids parasite. The mushroom that is High Charity was hollowed out to make the Covenant "Hole-y City", complete with a theme park, a church, several fast food outlets, theatres, etc. -the perfect tourist attraction. Shame it was ruined the AIDS virus.
High Charitypic

The giant mushroom itself

The Prophets ruled the tourist attraction for many years, though were kept out of public affairs (the threat of killing everyone inside with their boring speeches would've been bad for buisness). But evidently, the Prophets screwed everything up when they replaced the Elites with Brutes. The Elites lost their jobs and went on strike. This then turned into large scale rioting, quickly followed by civil war.

Just when things couldn't get worse for buisness, the AIDS virus invaded and took control of High Charity. When they tried to force the Prophets to sign a contract giving Gravemind complete control over High Charity, The Prophet of Mercy mumbled something offensive to the Flood (the word "water" apparently) and was killed for his heracy. Truth then fled, leaving the Hole-y City in Graveminds hands...tentacles...big long watchamacallits, you know.

The Flood evidently ruined High Charity's tourist appeal. No-one visited High Charity since the takeover, except Cortana, who Gravemind ended up having an affair with. Eww.

The Flood's piloting skills were quite terrible, and they ended up crashing it into The Ark. The Flood simply left High Charity there, where it was forgotten about for several years.

Master Chief had an annual pass ticket so he returned to the theme park one last time. Then he realised that the AIDS has completely ruined it so cortana decided to tell Master Chief to destroy the theme park so the Master Chief's annual pass was ruined.