The Karnak Temple in Luxor is over 4000 years old and built over 2000 years from 2055 BC. A cult temple dedicated to Amun, Mut and Khonsu, it is the largest religious building ever constructed, and can fit The Notre Dame Cathedrals and St Peter's in Milan just in the central temple walls.
The Ancient Egyptians believed that towards the end of annual agricultural cycle the gods and the earth became exhausted and required a fresh input of energy from the chaotic energy of the cosmos. This involved a 27 day regenerative festival called Opet and culminated in a procession to the Luxor Temple 2.4 km to the south through the avenue of sphinxes currently being restored.
Today it is still jaw-dropping, but imagine it in full colourful splendour and in prime condition. A must if you are visiting Egypt.