South Moeris Trireme
A mobile fort in the Faiyum Oasis.
This ship docks frequently at the Dioryx Megale Wharf, which is a perfect place to stage an ambush. There is, for example, a ballista there that faces the dock, but there are even stealthier ways to proceed.
As ever, the rope running from the stern to the mast is an ideal killing perch. Climb up the stern from the water, and simply wait for the captain to stroll by.
If you have to, you can then immediately dive to safety to avoid retribution, but while the ship is in dock, almost everyone will be facing landward, giving you the chance to kill with both ease and discretion. Doing so completes the location.