that's a cool find Tidbit, I've never seen that in game either. although the key glowies you have to click in some of the SS TFs you run look exactly liek that, except they're golden colored.
Here's a screenshot of one that I took while waiting for the others on a simulclick:
So... this is a key? I'd hate to see the keyhole...
MA Arcs - #67636, #92202
deviantart page
Slag Heap: Why you hurt Guardian!? Guardian no hurt you!
Heh, nice.
I actually added the monument's info to ParagonWiki; just hope there's no misunderstanding that leads to it being taken down being thought that it belongs in the Cathedral of Pain Trial info. 
I wonder if there's other monuments that can spawn...
Angry_Citizen made a thread about finding the Anger Monument a few weeks back IIRC, so we surmise that any of the IoPs can be spawned in the Shadow Shard.
I found a Destruction Monument now. Interesting.
The shard gets cooler and cooler.
I was exploring the Shadow Shard with my Stone Tanker (Giga Ton), when I saw an object that resembled an Item of Power.
To my disappointment, it was decor. Non-clickable.
Then, as I went around the Gravity Wells with Granite toggled (weee!), I reached what I thought was a dead end. I circled the rock-island and, to my surprise, found this.
It seems to pulsate every five to ten minutes with an unknown, non-combat-logged power called Hatred; this power is 35% Damage Debuff and yet an 6.67% (yes 6.67!) Recovery Buff - a little more than eight (3-slotted) Staminas!!
I did NOT doctor this screenshot, only blotched out my friend's chat handle.
Thank you devs for this cool, useless, totally random, and pretty part of the game that I never even knew about. We need to get more people into the Shard.