I went there about 10 years ago. As you come over the hill...you realize that the exit is approaching and suddenly you are there at the parking lot. The entire surroundings...360 degrees...looks like a cow field. There are no other structures other than the kiosk for tourists...perhaps planned that way.
I felt the unsettling effect as well. Our group was there for 90 minutes. I felt prepared to leave after 15 minutes. I will only say this in passing...I went to Dachau back in the mid 1980s...and felt the same way there. I will not make a comparison between the two...but it was the same precise feeling...needing to leave shortly after arrival. I've been to WW II cemetaries, Normandy, various castles throughout Europe, the Tower of London, and even the Shiloh battleground...none gave me that immedate feeling of needing to leave except those two locations.
My suspicion is that something else went on there besides the measurement of the year. Perhaps the early Celtics weren't the easy-going types that we often dream of.
I believe demonic spirits are in places where evil reigns. Human sacrifice is a horrific evil. That may be why you felt the way you did.
Cremation or sacrifice?
Definately. The reason that they needed to find the solstice is that is when they sacrificed their firstborn to Molluk (Molloch, Molokai, etc See Hislop for more info). The exact same ritual mentioned in the Bible.