From Discworld & Terry Pratchett Wiki
The reason for this land remaining largely under-developed in a city where space is at a premium is not hard to divine. Originally it is thought that this area was Ground Zero during the Mage Wars of remote antiquity. (As well as the time of the Sourcerer of recent amnesia). This not ideal situation has not been improved by the undeniable fact that it has been used as a dumping-ground by the University for at least two thousand years, in keeping with the general Ankh-Morpork ethos that once dumped, it's somebody else's problem.
Informally used as a gateway to the dimension inhabited by the Tooth Fairy, this area of the city has had a marked effect on speeding up the evolution of susceptible species such as rats, as well as the odd cat such as The Amazing Maurice, whose destiny it was to join forces with the rats and the stupid-looking kid in a major scam. It is also thought that Gaspode's particular talents are the result of seeking shelter in this area and foraging for what he could find.
However, with the development of the Thaumatological Park on the site, the area finally appears to be undergoing development suitable to its unique character and personality...
It is revealed that the witch Eskarina Smith maintains a cottage here. She appears to appreciate the challenge, as well as the temporally mobile cup-cakes.