The Monoliths of M'Soura, 25 km south-east of Asilah, form one of the world's few neolithic stone circles outside Britain — arranged in a perfect ellipse in an otherwise desolate landscape. You will need a local guide and a reliable vehicle to reach them.
The Roman ruins of Lixus, one of the Phoenicians' most successful settlements in Morocco, lie 5 km north of Larache. Less excavated and far less visited than Volubilis, Lixus has an atmospheric, slightly wild feel. A grand taxi from Asilah or Larache will get you there for a reasonable fare.