Though there are many private indoor pool and gym options, these can be very pricey. Facilities in a hotel are the best bet. For outdoor swimming, the best options are a day trip to Kilyos or Sile or Adalar which is closer.
Istanbul isn't known for its golfing but there are
a few courses nearby if you'd like to practice. Sailing is very popular in Istanbul
and there are a number of clubs that cater to various needs of both the novice
and professional. Click here to find out more.
http://www.crwflags.com/FOTW/FLAGS/tr~yc.html
There are also a number of dive centres that let you
brush up on your diving skills. For more information on diving schools and clubs
in and around Istanbul, click here.
http://www.dive-centers.net/
Fishing is another passtime of the Turks and the
Galata bridge is a favorite spot for fishing enthusiasts. Join the locals to
try your luck at the sport.