These are the two lowest levels from a larger wizard's tower map that's available, but they could be used in any scenario. In my campaign, there is a piece of paper on the floor near the entrance to the wine cellar that has a riddle. If the party figures out the riddle, which is related to the compass points on the ground, then the wall where the entrance to the sea caves opens and they gain entry. The riddle: “If these words you follow true the riddle will unveil to you a passage that will swiftly lead ‘down the hatch’ like wine and mead. So start your navigation then by the sailor’s star and hence begin. Then follow the nearest sun from dawn to dusk the day is done. To end the ride go towards the lower half of the equatorial divide until a new path you will find once all four waypoints are divined.” So if the party stands on or investigates "N", "E", "W", "S" in that order the riddle is solved and the party gains access to the sea caves. The caves include treasure, a way out to the sea by boat, and a mini-boss battle near the chest in the SE corner involving a sea hag and minions that try to drag the party into deeper waters. Have fun!