The quickest and easiest way to get to Yalova from Istanbul is to take a fast ferry  Fast ferries operate from Yenikapı (south of Sultanahmet), the voyage takes 70 minutes and costs 14 TL per person, 12 TL per person in vehicles, 67 TL for cars and 5 TL for bicycles. Concessions of about 1-2 TL is available for students and for those who buy their tickets online through İDO's (the ferry operator) website, as are early booking discounts.
There is a cheaper ferry line between Eskihisar just east of Istanbul and Topçular, about 30 km to east of Yalova. These ferries take about 45 minutes to cross the Gulf of Izmit and in 2010 it costs 45 TL for a car and 55 TL for a minibus, free for passengers within the car. Passengers without a vehicle pay 2.80 TL per person. You cannot book this service, you just turn up and pay when you get there. In Topçular, it’s possible to find minibuses heading for Yalova running on the highway lying just next to the harbour.
Visit the hot springs. There are many services offered.
Visit the market, opposite the Ferry terminal on the seafront. Open on Monday Wednesday and Saturday. A huge and superb selection of very fresh, mainly locally grown fruit and vegetables. Plus a good selection of other stalls
There are some tea gardens by the shore where you can also eat balık ekmek (a fish sandwiched inside half a bread).
The telephone code of Yalova is 226 (+90 226 when calling from out of Turkey). It used to be 216 prior to late 1990s, so old guidebooks may say so, which is not useful any more.