About 2 weeks ago I was riding my horse in the early evening in the purpose built menage at the stables where he is kept. The menage is flat, floodlit and overlooks 2 fields from the next farm and 2 of the fields from the farm where my horse is stabled. I was the only rider in the menage, and as soon as I entered the gate my horse started playing up - rearing, spooking, running sideways - especially as we got to the far right hand corner which overlooks the next farm's fields. I looked across and saw a grey horse with a rider in dark clothes, who appeared to be walking down a track between 2 of the fields.
I pushed my horse forward and whispered to him to calm down, but no sooner had we got to the next corner and he started again, only worse this time and he started snorting and sweating. When I looked to see if the horse and rider were scaring him, they were now at the very bottom of the field - but there was no way on earth they could have gone that distance in such a short space of time. The same thing happened again and again, every time I turned the figure had moved huge distances that no horse could have galloped. I then realised that this 'horse' and rider were not making any noise, and also began to wonder why they were riding in a pitch black field. I only saw them again once and then the vision vanished.
I decided the horse was too scared to ride so decided to turn him out for an hour in one of the fields with 2 other horses.
He usually hates coming in from the field, but had only been turned out about 20 minutes when a girl whose horse was out was bringing her horse in, and said that my horse was acting 'nuts', trying to jump the fence out of the field and looking terrified. I ran down to the field and he almost jumped the gate and was galloping around looking scared witless. Eventually I managed to catch him and put him in his stable and he calmed down after about 30 minutes.
I mentioned what I had seen to another girl at the farm and she asked me to show her which track I had seen the rider and horse on as she could not recall seeing a track recently that was still in use. The following day I took her to the menage in daylight and pointed at the track - which has been closed for about 2 years apparently and is so overgrown even a tractor would struggle to get down it!
Needless to say this confirmed that what I saw was definitely not of this world given that it made no noise and moved at an unearthly speed.
At the time I was cautious but not scared, but the horse most certainly was. Since telling people at the farm this story at least 2 other people have said their horses have acted similarly in the same place.