Gröna Lund is an amusement park with an excellent location. I recommend the attractions Eclipse, Katapulten or Kättingflygaren if you want to get an amazing view of the city as an added bonus. There are concerts more or less every night during summer here, often by world-famous artists such as Sting, Lenny Kravitz and Billy Idol.
If you are with a group of friends, you can compete in an organised pentathlon.
The park is open daily 12:00 – 22:00 from the end of April until the end of September.
There’s a plethora of restaurants to choose from, so you don’t run a risk of staying hungry. Kaskad lies next to the water and serves Italian food, but there are other options that serve German food (Biergarten). You can also find vegan options in most of the restaurants and kiosks.
There are many nice & convenient ways to get to Gröna Lund but my preferred option is to take the subway (green/red line) heading south from the central station and getting off at Slussen after about 3 minutes. Then it is a short walk to the ferry Djurgårdsfärjan which takes you from Slussen to Allmänna gränd. There are frequent departures and the crossing takes 12 minutes. The ferries are included in Stockholm’s public transport system and are traditionally built, which gives them a romantic feel. One other option I like is to take the tram (number 7, heading towards Djurgården Waldemarsudde) from the Central station and to hop off at Liljevalchs/Gröna Lund.