There are varying objects for each terrain type, along with a common list. Also, external creature dwellings will be covered. Mind you, I got lazy and I didn't clean up the repeats (such as the resource generators.) These were all taken from the scenario editor.
Name - The name of the object. If the name is in italics, it may only be visited once. If it's in bold italics it also vanishes upon visiting. It it is in bold it is replenished, usually every week. If it's name is underlined, it may be visited once by a particular hero. All others can be visited multiple times (That may not be a good thing, mind you.)
Image - The image of the object.
Effect - The effect of visiting this object.