Hi Anna
I would definitely recommend the Surf and Turf boat trip which Icmeler Travel Centre do. It's a super day out and it's all inclusive so excellent value for money (usually around £16).
You're driven to the other side of the penninsula (about 45 mins) to the boat, so you get to see some lovely scenery and villages along the way. The boat has a top deck with sunbeds for everyone (25-ish people), you get unlimited drinks and a barbecue lunch with village bread and delicious salads. The boat stops at a ruined monastery, the "American's House" and makes a couple of swimming stops in the afternoon - the sea at these stops is fantastic - crystal clear! It's a really relaxing day out. Leaves Icmeler at 9am and gets back at about 6pm.
I've done the trip several times as it's just such fantastic value for money and even if you're a non-swimmer you'll still enjoy it (my dad's done the trip a few times and he hates the water!)
Icmeler Travel Centre is situated in the centre of the resort opposite the Black Sea Restaurant - pop in and see Carol. A word of warning though - book early as it's so popular.
Mazz