The Great Hypostyle Hall at Karnak is one of the most overwhelming architectural experiences in Egypt. Walking among 134 enormous columns, each carved and painted with relief scenes, gives a sense of the weight and ambition of ancient Egyptian religious architecture that photographs cannot capture. The hall is partly open to the sky now, after the roof collapsed in antiquity, but even exposed it retains a sense of compression and density.
The reliefs on the columns and walls cover the standard Karnak repertoire of royal ritual and battle scenes, but the scale makes them different. The outer walls show Seti I's and Ramses II's military campaigns in considerable detail, including one of the most famous battle reliefs in Egypt. Give the hypostyle hall an hour at minimum, and consider returning to it during the evening sound and light show, when the columns are lit from below and the sky above provides natural drama.