On the stairs of the Opera house, facing the statue of a man on a horse. (In Sweden, a tip of about 10% is common in restaurants and taxis and also for guided tours. In Stockholm, both dollars and euros work fine. However, you should ONLY tip if you are satisfied with the tour and the service.)
The tour ends at the southern end of Kungsträdgården, a beautiful park in Stockholm. It is possible to take the tram to Djurgården, the "island of the museums", where among others, the Vasa museum, the Viking museum, the Abba museum and the outdoor museum Skansen are located.