In the Serpent Gorge (coordinates 258, 482) the pyramid of Pharaoh Khufu has risen from the sands.
Five sarcophagi stand around it. Dig up a sarcophagus (5 seconds) and a mummy rises from it. Sarcophagi left untouched sink back into the sand over time.
Khufu himself is a level 100 boss. After his death he respawns in 24 hours. Watch the timer on the Bosses page.
Event details are in the About section.