Central Siwa is dominated by the spectacular organic shapes of the remains of this 13th-century mud-brick fortress. Built from kershef (chunks of salt from the lake just outside town, mixed with rock and plastered in local clay), the labyrinth of huddled buildings was originally four or five storeys high and housed hundreds of people. A path leads over the slumping remnants, past the Old Mosque with its chimney-shaped minaret, to the top for panoramic views.