Have a look at my cache: GC1HAFT, "Der Konrad-Zuse-Cache" and GC1HRW9, "Konrad-Zuse-Bonus".
They are both in the same street area (big area), the Multi shows the cacher 12 letters (one letter at one tree), these are nessecary to calculate (A=1, B=2 ...) the final, and at the other final, of the bonus cache, you need these letters! A=N, B=O ... so e.g. the 12 letters are "five-four-zero" => The box is closed by chains, and there is a number lock with the combination "5-4-0" (e.g.)
Do it this way - and the cachers are enthusiastic!!