50/50 on what to think. The pyramids being a map of the stars is intriguing and shows how ancient man did some amazing things. But it could have also have been just a tomb, but why was it so plain and looked liked it wasn't used?
For reference I watched this video on it last night. The end of the video does get a bit ancient aliens-y but thankfully doesn't go too far. Great channel btw.
Wild Card Answer: They were indeed massive grain silos :ben-carson:
It most likely was not. It would line up with an display constellations inside, but that's because stars and constellations hold lost of significance in early religious traditions. You might enjoy Megalithic architecture of pre-celtic Europe if you want mounds built for star-seeing.