Triangular object - array of lights (multicoloured) - looked at it for about 20-30 seconds then it vanished

myself and a friend were driving back to glasgow from loch lomand (15miles north of glasgow) along a wooded coutry road around the time I mentioned above.  As we passed over a slight hill after rounding a bend, I noticed on the right hand side of the road, behind some trees an array of lights and what appeared to be a large triangular shape.  It looked very bright and as I was looking at it rose up above the trees and basically vanished.  When I say vanished, i did not see it actually go anywhere, it just wasn;t there any more.  I drove on for about 2 miles without saying anything to my friend, then asked him if he had 'seen that' he agreed that he had and that it was the same shape etc.  I would estimate the size to be around that of two double decker buses on top of each other.
Date is approximate.  PD