Don't be shocked by the Terrain rating, that value was checked in advance with the approver to be the correct rating in that case. It is not because of needed Jeeps, Boats or climbing equipment, but you need a WLAN device (PDA, Notebook,...) and - of course - the skills to use it.
Additionally please do the whole cache in stealth mode, people sometimes get nervous watching others with electronic equipment in public. The cache leads through an area of flats, so please keep caching-groups small ;-))) The route can be done by car, walk the last ~100 meters.
Stage 1: "The Old Ones"
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N1 48° 08.003 E1 016° 28.507
You start at some "old technology" which has (unfortunately) no MAC-Address to identify 
, but a four-digit-number will do it as well. Take that number and make a prime number breakdown:
"A" should be the smallest factor, "B" should be the biggest factor.
Stage 2: "The Modern Ones"
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N2 = N1 - 2*B + 15*A
E2 = E1 + 5*(B - 3*A) + 4
Sit down.
Think of the name of the cache and try to "hear" something. There are many "in the air", one of them has a (german) number in the name. Convert all 6 characters into numbers (a=1, b=2, ..., z=26), sum them up and add 11. The left digit of that value is "C", the right digit is "D".
IMPORTANT: Just listen, no connecting or attempting to get in is neccessary here !!! Depending on your equipment, you will "hear" it loud or soft, sorry in advance if there is inconvenience at that stage ...
Cache: -----------------------------------------
N_cache = N1 - A*B - C*D + 18
E_cache = E1 + A*B*C + 2*C*D - 13
The Cache is a Film-Canister, please bring your pen with you.
HAPPY CACHING
EarlGrey