There are a handful of caches around where accurate co-ordinates of the cache are not available, but rather the best co-ordinates you get (either on the cache page or after solving are puzzle) are something close to the cache & then you've got to find the cache yourself. I personally don't enjoy these caches, although understand that others might.
The guidelines for hiding a cache were recently changed to include the following statement:
Doesn't this mean that hiders must make an effort to provide accurate co-ordinates and it's not sufficient to say "It's somewhere in the park" or "It's hidden somewhere in the wall".You as the owner of the cache must visit the site and obtain the coordinates with a GPS. If time allows take several reading at different times over a few days and average the results. This will help you achieve greater accuracy on your coordinates. GPS usage is an essential element of geocaching. Therefore, although it is possible to find a cache without a GPS, the option of using accurate GPS coordinates as an integral part of the cache hunt must be demonstrated for all physical cache submissions.
Disclaimer 1: I'm only referring to gc.com caches, of course gca caches are ambivalent to this.
Disclaimer 2: For those who've placed caches of this type: I do appreciate the contribution you've made by hiding your cache, I'm just discussing this, not criticising your cache.