Standing at the start coordinates, you have a large parking lot behind you and a door in front of you. To find this geocache, you need to enter the door and find out some information. The door is not always open, though. Check the end of the cache description for opening hours.
It is commonly thought that the building ahead of you is a museum, but in fact it is the remains of an epic battle. A long time ago, at the dawn of flight there was a man called Carl Cederström who ushered in the era of flight in Sweden. This went well for some time but he soon attracted the attention of evil time lords from the future. They wanted to stop him from flying since that might in the end endanger their future evil empire. And since this is a time travel story, you now need to imagine wavy lines appearing across reality and a change of story tense...
You are air pilot Carl Cederström, and it is time to enter the hangar. It is a large building straight ahead of you. Your plane is in the hangar to the left, somewhere in the furthest parts. You never quite know where to find it since the mechanics seem to park it in a different place each day. It's usually easy to find, though, since it's the only plane that is painted bright yellow and red.
As you are climbing into your plane, a warning bell goes off. It's the "intruders from the future" alarm! That's not supposed to go off until tomorrow, at the earliest! That means that you need to find the defense codes that have been cleverly hidden around the area. Once you have the codes, you can enter your name in the "stop the intruders" ledger that is stored at a safe place. The problem is that you don't know where, but you think that the defense codes will tell you this. To begin with, your plane has the code ABCD painted on its body, so rush out of your plane again to note that. Apparently the yellow and red plane is currently hidden away in a non-accessible hangar. Use ABCD=5558 in the mean time.
Then you need to run to the jet engine (whatever that is; maybe a future you will know some time) that you passed on your way to your plane to get another part of the cleverly hidden defense code. To the left of that engine is a jet plane prototype you hope to live to see some day. It's unusual since it's only built at EF% of the real plane's scale. It had a flying time of GHI hours in total. Due to construction, the down-scaled plane is not available. EF=70, GHI=286.
The next two parts of the code are hidden underground. As you come down in the secret catacombs under the air field, there is a room to your left with a sign above the entrance reading "HEMLIGA HANDLINGAR". Enter here and follow the corridor to the right. Look into the room at your left and read the code "TTV-JKL" on one of the secret missiles hidden here.
Then exit via the portal opposite this room and continue straight ahead until you have a picture showing a number of people to your left (this is the first picture on that wall). Count the number of faces, which is M. Continue ahead and go to picture number M on your left. This picture will tell you another part of the defense code, in the form of a word in quotes. Find the place in the alphabet for each letter in the word and sum them, giving you NOP.
Now go up to ground level again and go into the right part of the hangar. Somewhere in here is a plane with the identification number "29970" written on its body that you need to find. As you find it, you can see that the enemy from the future has already arrived. Straight ahead of the plane with "29970" on it (and at the same height) is an enemy plane which has already stolen one part of the defense code, but it's still visible in red on its body: QRS.
You now have all the information that you need which is good since the enemy apparently already is here! You just need to do some math:
XXXX = ABCD - (P * GHI) + 239
YYYY = EF + JKL + NOP + QRS + 682
The "stop the intruders" ledger must then be located at N58 2X.XXX E015 3Y.YYY! Go there quickly and write your name in it. You have been told that writing in that ledger will stop plane time so that the enemy will stay suspended in the air forever, unable to harm you. Unfortunately that also means that you can't continue flying. Perhaps you could try a new career as a geocacher? You seem to be good at that!
Opening hours for the building:
Wednesday-Sunday: 10.00-16.00
Thursdays: 10:00-19.00
Closed on the following holidays: New year's eve, New year's day, good Friday, easter Saturday, May 1st, Midsummer's eve, Christmas eve and Christmas day