Verified answer

There used to be "sea bus" ferry some time ago from Yenikapi to Sile, but it doesn't run anymore.

The site below gives the good information about the beaches with transportation options around European side.

http://www.turkeytravelplanner.com/go/Istanbul/Sig...

Last summer, I went to Sile couple of times by car. We stopped by some local restaurants. It was the good opportunity to got to know local people. If you do the same try delicious Gözleme and Ayran(Yogurt Drink).

http://www.turkeytravelplanner.com/details/Food/go...

Hope this helps.

Sile is 60km from Istanbul. From the European side of Istanbul, you need to pass the Fatih Bridge on the Bosphorus, and follow the highway output connections with Umraniye to Sile, following Omerli direction and continue in the direction of the new Sile road, you can reach there in 45 minutes.

By public transport, you need to take "139A" bus from Uskudar, which goes to Sile and Agva. There's a bus to Sile, every day per hour.

But, instead of Sile, I would recommend you to go to the Prince Islands (especially the Big Island-Büyükada!) There are plenty of beaches, you can rent a bicycle on the island for very cheap price. You can go to the Prince Islands (Adalar) from the Kabatas Port.