I recently read A Colder War, a contemporary spy novel by Charles Cumming, a Scottish writer. Rather good it was too. I'll be looking into his back catalogue.
Blue Mosque, Basilica Cisterns, Topkapi Palace, Grand Bazaar, and a ferry ride. If you want a restaurant recommendation, my favourite is Pasazade, especially for the Mutancene (Ottoman lamb stew with apricots and almonds). A truly great city.
Suomenlinna island in Helsinki harbour is worth a visit. The ferry only takes about 20 minutes.
in Tallinn, don't miss DM Baar, the Depeche Mode themed bar/night club, just off the main square. Fabulous !