(Click to embiggen of course)
For all the coolness that this is, I would be remiss in not informing you that it is one of many monuments to World War II veterans erected in what was then Yugoslavia under a program by Marshal Tito. There is a website devoted to those veterans.
Now for another image:
You can find more by a google image search
I could go on about their abstract majesty and how their neglect adds to their appeal and mystery, but a random table would be more useful, don't you think? Here's one for you to riff off of for the "purpose" of your spomenik.
- Temple of Tharizdun (or a local equivalent if you prefer.) Is it active? Abandoned? Waiting for the PCs to be sacrificed?
- Confluence of ley lines. Use another table for how magic is f'd with here.
- Portal to another plane. I'm sure there's a table for random planes somewhere.
- Another entrance to your megadungeon. If you don't have one, now you can.
- It is sentient.
- It is the local appearance of the Sphinx.
- Another wizard's tower.
- Home to a deity. Go get Judges Guild's "Unknown Gods." Or J. Mal's Petty Gods
- Home to a Deck of Many Things.
- Home to the Maid, Mother and Crone.
- A brain transference station left by the Elder Ones.
- Landing site for the Githyanki invasion. If the PCs press the red button, they unwittingly have reopened the locked passage.
- Holy site for the Gathering of the Tribes. Which tribes? You want me to do your job for you?
- Death is waiting here to play chess with you.
- Prison for the vice (1d8: 1 Lust 2 Gluttony 3 Greed 4 Sloth 5 Acedia (irreverence to your deity) 6 Wrath 7 Envy 8 Pride). All within the influence of the monument must save or become possessed by the vice.
- An alchemical mechanism for turning base substances into gold. It's location and possession is highly coveted by many powerful sorcerers.
- Home to an artifact and its guardian.
- A wolf in sheep's clothing. A mimic basically. It uses its appearance to attract PCs and eat their magic items.
- A Tomb. Is it the Tomb of Horrors, or another?
- A monument to war dead.
For reading through all those, you get another picture: