I've been to Stonehenge once when it didn't kill me in one form or another...
Mining... well, I usually don't risk it, but when I do, I get one gem... and yes, it wass decreasing. they usually get lost in some special events. But now it seems to be staying in the same place...
And exp, I've had days where it only goes down. But considering you get exp from the forest, the main center of the game's action, of course your exp is supposed to go up continuously.
I try to look on the bright side, just sometimes it's kinda hard to see...