AVENGERS ASSEMBLE!
PLEASE NOTE THERE IS NO LONGER A BONUS CACHE. THE FOLLOWING INFORMATION IS JUST HERE FOR FUN.
"Avengers, this is Director Nick Fury of S.H.I.E.L.D. I have been taken hostage by Loki and I need all of you Avengers to work together to rescue me. I have left you each a clue which, when put together, will lead you to my whereabouts. They have been scattered far and wide as I cannot risk my position being revealed to any other villains. Each location will bear some relevance to the Avenger it is intended for. I trust you will not fail me in my hour of need. When you have all 6 clues you will be able to decipher the coded co-ordinates which are on the 'Avengers Assemble- Nick Fury' page (GC62NKR). When you discover where he is holding me you will see that the God of Mischief has a sick sense of humour indeed. If all 6 clues have not been found and all 6 locations visited and logged then Loki will delete your log at the Final Location. Good luck Avengers."
The relevance for Iron Man's cache is that it is opposite the Science Park and Tony Stark is, of course, a brilliant scientist.
Please be aware of muggles, replace as found and remember to collect the clue from the logbook.