From the Groundspeak Guidelines
A challenge cache requires that geocachers meet a geocaching-related qualification or series of tasks before the challenge cache can be logged. An example is finding a cache starting with each letter of the Alphabet.
The CHALLENGE:
You have to prove that you have found 9 different types of caches that start with the letters in the word ‘CHALLENGE’. There are 9 letters in the word and you can use one type only once. Add the list of your suitable founds with the types, GC-codes and the date you logged preferably with links to your ‘found it’-logs. You may count any cache type you see fit to fulfil these requirements. In addition, previous finds also count toward fulfilment of this challenge. When you have completed the challenge, please provide a list of your qualifying caches, via GSAK or your statistics from Geocaching.com
Example:
C = Capital Catch Up - Event - GC21XDT - 28.12.09
H = Horse laugh - Letterbox - GC2P0WT - 17.04.12
A = A Byte and a Half at Atiu 100000 - Traditional - GC36VHV - 12.10.12
L = Lotsa Bridges - Multi - GC2RX4C - 19.04.11
L = Lighten Up - Virtual - GCM408 - 13.04.12
E = E L O - Unknown - GC4HDZA - 17.08.13
N = NZ MEGA Auckland 2013 - Mega - GC44FC9 - 28.10.13
G = Gold - Earth - GC23BVR - 24.04.11
E = Eddie’s Lost Lunchbox - Wherigo - 28.10.13
The cache is a small brown screw top plastic jar, containing a log-book.
Please bring your own pen.