Menelaite Trireme
A lootable ship in the northeast of Alexandria. The setup is pretty simple- a handful of guards on board, the sole treasure in the central command tent.
Most of the guards don't look at each other (long sea voyages will do that do a man), so you can usually just take out one, then sneak in for the loot- a red chest by the bedding.
Claim it to complete the location.