Hi Lotus
You could definitely combine a side trip to Yemen from Cairo. If you're interested in architecture, then the tower houses of Old Sana'a will be a life highlight. Yemenia, the national airline of Yemen, has return flights from Cairo to Sana'a as does EgyptAir. The flight time is about 3 hours.
Travel by sea - if you could find a freighter that would take you - is something you wouldn't want to do.........
Aziza in Dubai