Don't know whether to call Fayoum an oasis or not, technically it is, because there is desert between it and the Nile, and a lot of it's water comes from springs. It is far too big to be an oasis though. Anyway, whatever it is, it is about 80 Kms South West of Cairo, and has a huge salt water lake called Lake Qarun. It is mostly an agricultural community, and in the past 20 years, irrigation water from all the farms were redirected to a valley to the South of Fayoum, called Wadi El Rayyan, that valley now has two gigantic fresh water lakes in the middle of the desert. Fayoum also has lots of ancient artifacts and sites such as Madinet Madi, Dar Qarun, and Kom El Atl.
Wadi El Rayyan is a valley in the middle of the Fayoum desert, that is now totally covered by two gigantic fresh water lakes, the two lakes have different altitudes, and therefore a waterfall was created where they meet. There seems to be no end to this water, and the level of it has gone up at least 5 or 6 meters from when I first went there in 1994 till I left Egypt in '97
The real story behind Qasr Qarun is not as interesting as the legend made by the locals. They say that this is where a pharaoh (Qarun) who was known to have lots of wealth, used to keep his wealth, and even the caretaker while showing us around, was pointing out the holes in the walls where the jewels and treasures were placed