den sure kalkun: Archived. The solution to this one was mostly in the title. "Bridge" is not just a structure for transporting water, people and vehicles over something, it is also a card game. "Below the line" is something that is meaningful in bridge: the points a team can score are described as "above the line" or "below the line".
2500 is the postcode for Valby.
The cache was hidden in the doorway of Valby Bridge club, which is on the first floor of its building. Hence "under bridge".
The geochecker was fairly kind, so you just needed to have the rough place for the bridge club to be given the final coordinates. Trouble is, there weren't any bridges nearby, so it wasn't so easy to guess just by finding bridges in Valby [;)]
Thanks to all who visited, especially Jens who came incredibly close to an FTF without knowing a new cache existed. Cruel luck for you; I didn't know to time it to be released just at that time, but if I had known, I would have done it just like that [^]