When you don't have the strenght to walk around Stockholm on foot or want to make day trips ouside the city, then a boat trip is a good idea.
The Stockholm ā la Carté card allows you to make
Boat Trip to Drottningholm
Travel to the castle Drottningholm just outside Stockholm. The boat departs from Stadshusbron to Drottningholm. The trip takes 50 minutes one way.
Boat trip to Fjäderholmarna
Fjäderholmarna is sometimes called "the closest island in Stockholms archipelago". The travel times is only 30 minutes. One the island you'll be able to swim, visit local craftsman or go to the restaurant.
Steam boat to Mariefred
For 100 years now, the steam boat S/S Mariefred has travelled the same route between Stockholm - Gripsholm Castle in Mariefred.
The travel time to Mariefred is 3,5 hour one way but restaurant and café is available onboard.
Tickets are available to collect at the ticket both 15 minutes before departure at the latest.