I have two explored ruins on my map with a crazy bright, sun like pillar of light above them.

I have no quest to them, and I can't explore them again.

What is that light?

(I'm on the latest patch on Steam with all the expansions purchased.)

If the light you are talking about shines straight down onto the ruin, as oppose to an angle like the quest markers, and has a slightly orange tint, then these are the "Victory Quest Markers."

As soon as any player in the game finishes the last step of their faction quest, they unlock the first step of the Victory Quest. As part of that quest, they need to search certain ruins, which are revealed for all players (So that you have a chance of stopping them from achieving their goal.)



Edit: Here's a picture of the victory quest marker.

That was it, thank you!