In order to find this cache, you must first complete the Adventure Lab The Hunt for Pink December.
This Adventure Lab does not work in quite the same way as most other Adventure Labs. Go to the first stage posted. In the description of the first stage you will find a Youtube link which will show you where the mysterious pink cacher went. Use this to get to the spot where the information you need is located (the posted locations for all the later stages are fake; you need to watch the films to get to the right spot).
When you have completed all five stages of the Adventure Lab you will know where the mysterious pink cacher has hidden the treasure.
If you liked this ALC, there's another similar one in Alingsås: Kaféstaden Alingsås