Mystery cave

Every city has a Mysterious cave. It is located right above the buildingsite on the left side of your Castle. You can invetigate it by clicking on it. This is only possible if you see "the eyes" in the cave.

Right after you investigate the cave, you receive an email. The outcome can be very different:
 * You've unleashed a swarm of flesh eating cockroaches unto your city! xxx citizens died as a result of the infestation.
 * You've discovered a stash of xx Dragon Crystals.
 * You found a stray Dragon inside the mystery cave. It has joined the ranks of your army!
 * Congratulations! You've discovered a stash of xxx Lumber!
 * You've discovered treasure inside the cave worth xxx gold!
 * Your investigation team rescued a group of xx lost and hungry Scouts from the cave, they have joined the ranks of your army!
 * Your investigation team found nothing of interest inside the cave.