Gothenburg hosts 1 festival in this guide: Way Out West.
Gothenburg has 1 festival in this guide. They run in August, and festival-day temperatures range from 21°C (70°F) to 21°C (70°F), with nights down to 14°C (57°F). That range is the reason there is no single "Gothenburg festival outfit". The answer changes by month and by site.
1 carries a high rain risk, which makes waterproof footwear a requirement rather than a precaution.
The ground matters as much as the sky. Every festival here is on city park, which puts broken-in trainers or a low boot at the top of the list for most of these events. None of them have camping on site, so you are travelling in and out each day and the outfit has to survive the journey at both ends.
Stylistically the crowd here leans indie, streetwear, elegant and alt. Way Out West is the largest of them at around 35,000 people, and it sets the tone the smaller ones react to. None of that is a dress code. It is what you will see, which is worth knowing if you would rather blend in or deliberately not.
