I found the following information on Wikipedia:

The SS Thistledorm left Glasgow on her final voyage on 2 June 1941, destined for Alexandria, Egypt. The ship's cargo included: Bedford trucks, armoured vehicles, Norton and BSA motorcycles, Bren guns, cases of ammunition, and rifles as well as radio equipment, Wellington boots, aircraft parts, railway wagons, and two steam locomotives. It was bombed by the Luftwaffe on October 6, and sank to the bottom.  

In the early 1950s, Jacques Cousteau discovered her by using information from local fishermen. He raised several items from the wreck, including a motorcycle, the captain's safe, and the ship's bell. The February 1956 edition of National Geographic clearly shows the ship's bell in place and Cousteau's divers in the ship's lantern room. Cousteau documented diving on the wreck in part of his book The Living Sea.

Following Cousteau's visit, the site was forgotten about except by local fishermen. In the early 1990s, Sharm el-Sheikh began to develop as a diving resort. Recreational diving on Thistlegorm restarted following the visit of the dive boat Poolster, using information from another Israeli fishing boat captain.

The massive explosion that sank her had blown much of her midships superstructure away and makes the wreck very accessible to divers. The depth of around 30 m (100 feet) at its deepest is ideal for diving without the need for specialist equipment and training.

The wreck attracts many divers for the amount of the cargo that can be seen and explored. Boots and motorcycles are visible in Hold No. 1. Trucks, motorcycles, Wellington boots, rifles, Westland Lysander wings, about twenty Bristol Mercury radial engine exhaust rings and a handful of cylinders and Bristol Blenheim bomber tailplanes are visible in Hold No. 2. Universal Carrier armoured vehicles, RAF trolley accumulators, and two Pundit Lights can also be found. Off to the port side of the wreck level with the blast area can be found one of the steam locomotives which had been stored as deck cargo and the other locomotive is off the starboard side level with Hold No. 2.

In 2007 The Times named Thistlegorm as one of the top ten wreck diving sites in the world.  It was certainly the best wreck site I have ever dived.