Throughout your various journeys, be on the lookout for large red glyphs on the ground like the one in the achievement pic. These are the secrets you need to unlock. They are incredibly faded at first, blending in well with the dirt. The key is to kill a few enemies that are standing on it. You may need to kite them over, but after say 10 or so sacrifices, you'll be rewarded with some treasure and probably an item as well. The glyphs will glow brighter with each kill and fade over time, so act quickly.