This geocache requires two people, to find it: it is not possible to do it alone. Find a friend, and persuade them to help. Take mobile phones (you'll want to be able to check in with one another) and writing materials and/or a calculator (there'll be a tiny bit of addition required).
One of you must travel to the waypoint called Box One. The other must travel to the waypoint called Box Two. You must do this at the same time: if you try to visit one, and then the other, you will not be able to find the coordinates of the Final Stage.
(Note: Box Two is at this cache's published coordinates.)>
Box One is on the Wheatley side of Horspath, in a forested area where formerly stood the route of the Wycombe Railway/Great Western Railway: the tracks were dismantled and removed in the 1960s - nearby GC1M5Z5 is worth a visit. Box Two is at the edge of beautiful Bagley Woods: if you get the chance while there, you might also like to visit one of my favourite Oxford caches, GC3X275.
At both Box One and Box Two, you'll each find a 2-litre camouflaged tupperware container. Inside the container you'll find a special piece of equipment and instructions on how to use it. Follow the instructions, discuss the results with your friend, and you'll soon discover the coordinates of the Final Stage (please leave the instructions and the piece of equipment as you found them, for the next visitor). No special knowledge is required.
Aside from a log book, pen, and tradables, the cache initially contains two "first to find" prizes: one for you and one for your friend (you can decide between you who gets each).
Parking: For Box One, you might find on-road parking in Horspath or Wheatley, or else there's a wonderful footpath that connects over Shotover Hill from Thornhill Park & Ride: an enjoyable hike with a handful of geocaches on the way. Box Two is not, contrary to what a map might have you believe, easily accessible by road: you might like to park in Kennington village (which has plenty of freely-available on-street parking) and walk. The final stage is only accessible by foot (or, for the adventurous, by bicycle).
Frequently asked questions
Do I really need a second person?
Yes, you absolutely need a second person to solve this cache, unless you're capable of being in two places at the very same moment. The only way around this would be either to break the law (don't do that) or to break the rules of geocaching (definitely don't do that).
Do both people need a GPSr?
It'll be easiest if they do. If you've only got one GPSr, then you can "drop off" your friend at Box One or Box Two, then travel on (with the GPSr) to the other waypoint alone. It'll take longer, but yes: you can get by with just one GPSr.
Do both people need a mobile phone?
It'll be harder if they don't. If you want to try without mobile phones, then here's what you need to do: (1) synchronise your watches; (2) agree to arrive at the waypoints and get the information there at exactly the same time; (3) meet up afterwards and share the information you collected, in order to solve the cache.
Do we have to find the cache on the same day as we find the boxes?
No. You must visit Box One and Box Two at the same time... but once you've done that, you'll have the coordinates of the cache and you you can visit it whenever you like. So if you want to do this cache over two separate days, that's easy: spend the first day (with a friend) collectively finding Box One and Box Two, then spend the second day finding the actual cache.
Why are there no hints?
If you're at the right coordinates, you probably won't need them: Box One and Box Two are both larger than the average cache for this part of the country, so apart from having to look underneath or behind a couple of things, you shouldn't have any trouble. If your coordinates for the Final Stage aren't about a kilometre and a half away from the published coordinates, they're wrong: but it's very unlikely that you'd accidentally get the "wrong" coordinates and be out by only a little - you'd be more likely to be out by a lot... and when you get to the Final Stage coordinates, it's pretty obvious where the cache must be hidden. I don't think a hint is needed.
This was the most awesome cache ever. How can I make one like it?
Once I've verified that you found this cache, I'm happy to share with you all of the secrets you'll need to make another cache in a similar style If you do so, please consider setting it up elsewhere in the world, so that others can also enjoy this unusual experience, and please consider referencing this one as the original.
Don't have any friends who're into geocaching? Check the notes logged against this cache: there could be other local players who are looking to tag-team: or write a note yourself and seek a local cacher to be your buddy: remember - you can't do it alone!