As it is now, all resources are revealed on the map at the start of the game. While this is fine for the more 'normal' resources, say fertile lands and old growth forests, it makes less sense for special buildings like ancient temples and lost libraries. I mean, how can you tell from afar that a certain tower contains vast stores of knowledge, are there roadsigns or something? And wouldn't these kind of buildings attract some attention, human or otherwise?

I propose that these kind of resources all look like any other Ancient Ruin/Old Tower/Buried Temple/etc adventure site until you investigate them. This would make finding one of these sites feel a lot more special.

You could for instance recieve a quest from some guy that used to live in an old tower full of books, but was recently kicked out by a band of bandits. Dismayed that he will never be able to find out if Bella will end up with Edward, he asks you to help him recover his precious novels. After clearing the bandits out, you realise that the tower might contain valuable information, and voila, one 'lost library' is revealed on the map.

Or you could just wander onto some ruins, and be attacked by a mad alchemist. After defeating him, you discover that he was there for some of the magic knowledge stored at that place, and one Ancient Temple is revealed.

Perhaps some of the 'normal' resources should be defended as well. For example, an Old Growth Forrest could be home to a bear, a pack of wolves, or a swarm of ravenous pixies. This wouldn't mean that most resources are very difficult to acquire, but it would be a little more involved than just building a town nearby and waiting until your influence covers the tile.