Algiers:
Algiers has been a port since Roman times, and due to the dry desert climate has some good ruins to see at Djemilia and Timgad. Plus there are many beautiful Turkish houses and mosques, and a myriad or alleyways to explore.
Tipasa:
Situated along the cost from Algiers has exceptional Roman, Punic and Christian ruins, and a Numidian mausoleum.