Happens Twice every year, 22nd February and 22nd October)
Abu Simbel is located in the heart of Nubia and is accessible by road or air from Aswan. The most remarkable feature of the site is that the temple is precisely oriented so that twice every year, on 22 February and 22 October, the first rays of the morning sun shine down the entire length of the temple-cave to illuminate the back wall of the innermost shrine and the statues of the four gods seated there.
Ramses II, in a fit of precision and despotic architectural egotism, carefully angled his temple at Abu Simbel so that the inner sanctum would light up twice a year: once on the anniversary of his rise to the throne, and once on his birthday. The combination of human endeavour and natural phenomena provides what must be one of the most spectacular sights in the world.
For more on this unique event
http://www.abu-simbel.world-guides.com/abu_simbel_events.html