Wary Jere's Ghostly Tale

We were swapping ghost stories over beers back in Bimini. A friend told one where a figure passed right through her. She was on acid at the time. That has to be taken into consideration. However, her tale sparked my memory, although it took a while to make the connection. 
My incident occurred in the early 70’s when I was backpacking in South America with two friends. We were in south central Colombia; the middle of nowhere. We’d ridden all day in an ancient bus to reach San Augustin, perched high up in the Andes in an archeological zone. Pre-Colombian ruins poked through the mists rolling off dark craggy peaks. Psilocybin mushrooms grew in abundance. It was a pretty cool place. 
The crumbling town was inhabited by descendants of the Aztecs. I met my companions for dinner at a small hotel across from the wind blown plaza that had a little restaurant inside. When we arrived, the place was packed with gringos and a party was in full swing. It was someone’s birthday. We ate our meal and shared some chocolate birthday cake. Then a jug of tea was passed around: Mushroom tea. I wasn’t into that, but took a sip to be polite. 
My mates and I then parted company. It must’ve been around 10:00 p.m. when I arrived back at the little room I had rented on the main street. Four whitewashed walls, a slat bed and a chair, plus a candle. The second my head hit the hard bed, the acid came on. The high was strong but mellow. Sleep was out and being cooped up in a coffin-size room was suffocating, so I decided to take a walk. I hit the gravel road and turned right, one foot following the other. Twenty minutes later, the town was behind me on a road that headed up towards a towering mountain silhouetted against the rising moon. The night was pleasant, so I continued walking. An hour later, I could see the lights of San Augustin far below me.  
I felt energized and wondered how far up the mountain the steep switchback road went, so I kept going. Just shy of the summit, I paused to catch my breath. That’s when I heard a faint grunt coming from up the road that would fade then return a little louder. I stood there on the narrow lane waiting, when I spied something dark heading towards me and jumped to the side just as a large pig trotted past me. 
I wondered where it could have come from. This was a protected zone with no farms or people. I peered over the edge of the switchback and waited for the creature to pass below. It never did. Curious, I moved back down towards the curve it had disappeared around. Nothing. Then a rustle came from an area to my left where I could make out a little cleft in the rock. I felt it as much as I heard it. It was like a whisper. Soft. Inviting. I inched towards the spot and got within a few yards when every hair on my body suddenly stood at attention while every cell screamed “Run!" Run I did. I covered half the distance back to town before I slowed down. My panic was instinctive. Ancient. Ancestral. I’d seen nothing, but I can still remember that bone chilling whisper. Even today.