The Tallinn Card
If you intend to do more than roll out of your hotel bed and into the nearest pub, you might want to consider investing in the 'Tallinn Card'. It's not quite the same as having the mayor hand you the keys to the city, but it could be the next best thing. The 250 kroon outlay you make for a 24hr card will almost certainly be made back the minute you step into your second site of the day. If you're staying in town shorter or longer there are also 6, 24, 48 and 72 hour cards to sate your need for a bargain.
Throw in a free sightseeing tour of the Old Town, squillions of discounts at shops, restaurants etc, free spa visits, bowling and go-carting - and even free admission to the notorious Hollywood club - and you're onto a winner. With the card, you get an over 100-page booklet (available in several languages) describing the over-100 destinations the card applies to, their opening hours and location on a map. It's not only handy, but also makes for a nice souvenir of the city.
See the official website for full costs and details.