Wednesday afternoon, between 18.00 and 20.00, I was lying in a park here in Logrono, basking in the sunlight. The air was clear; it was not too hot. Not a cloud in sight. For a while I lay with my eyers closed. Around 19.00 I opened my eyes and looked up in the sky. I looked at all the birds flying above me, the dust particles drifting around, the passenger airplanes passing to and from Bilbao and simply enjoyed myself. The sun was shining directly on my head; I didn't see the sun when gazing straight upwards, it was just above my eyes. In other words, my view of the sky was as perfect as it gets that time of day here in Logrono. Then, a thought of ufos passed my mind, and in that second, a white dot materialized above me, far far up in the sky. It travelled in a straight line very very fast, but not too fast for my eyes too follow. It travelled in a straight line from north to south. Since my sight had already been calibrated by the birds at different altitudes, airplanes and dust particles of different kinds, I could clearly see that it was not any of those things, that is birds, airplanes or dust particles. I could also clearly see that it was very high up in the sky, higher up than passenger airplanes travel. It also moved much faster than an average passenger airplane. In some seconds, it was gone on the southern horizon, due to the air getting 'thicker' towards the horizon. I was very calm, but I understood what I had just seen, even if it was hard to believe. Some minutes passed, and I started to doubt my own perception and my interpretation of it, thinking it was probably just a bird or something. As soon as I had thought this, a new one appeared, at the same spot, travelling in the same direction at the same speed. Now I noticed, while I was watching it, that as long as I was was actually observing it, there was no doubt whatsoever that this was not a bird, airplane or dust particle. Also, I noticed that I was fully alert, registering as much as I possibly could, and not in any way 'shaken' by the sight. Then it was gone. And then, in some minutes, came the doubt as to what I had seen. Maybe it was a low flying satelite, reflecting the sun? Again I was 'in limbo' concerning what I'd just seen. Some minutes later, and a third one 'materialized' just above me, like the other two, travelling at the same speed (tremendous), altitude and trajectory. Before it disappeared from sight, I thought 'why don't you make a turn, so I'll know you're not a satelite?' And at that very moment, it made a turn (to the west)!!! Then it was out of sight. Then a cessna plane or something of that kind came flying low over me, followed by a fourth ufo, same as the ones before. But before this one vanished over the horizon, a passenger airplane came along. Their trajectories crossed, and now it was plain to see that the ufo was flying much higher, and much much faster than the passenger airplane. Btw, the ufos were white dots, very small, yet very visible, but only for those looking intently up at the sky at the very place where they were flying. I would say they were circular, but that's hard to tell at such distance. They were, or seemed at any rate, very solid, white things, with no discernible shape. Again, the ufo disappeared, and again the doubt came sneeking up on me. And then came another, and then another, until the doubt seemed more like vanity than anything scientifically substantial. All in all, I saw ten such ufos in the span of half an hour. I never saw two at the same time, but at one time a new one appeared immediately after the last one disappeared over the horizon, so I guess it must have been at least two, but probably ten, unless the same ufo flew over me until out of sight, and then teleported back to just above me, doing this ten times. One of the ufos had more of a west/east trajectory, the others more or less in a straight north/south trajectory.After the ufos had passed, i noticed a small cloud, of the cummulus kind, with lots of creases and shapes, the type of cloud you see faces and stuff in, moving towards me from the south-east towards north-west. I was baffled by the speed at which it 'unfolded'; in a minute or two it had tripled or quadrupled it's size. It looked, visually that is, far more astonishing than the ufos. As it had dramatically increased it's size, it turned into a uniform foggy patch in a matter of seconds. It went from being your average type of cartoon-cummulus to an elongated circular patch of uniform 'fog' in probably no more than two minutes, expanding it's area by probably 600-1000% in that time span. The transformation happened just above me, where i'd seen the ufos 'materialize' earlier, but at much lower altitude, maybe a fifth of the altitude of the ufos, although that is only a guesstimation.I believe I've answered point 1-3 above.4: White dots, most probably circular. Moved in straight trajectories from north to south at very high speeds, took maybe 10 seconds to cross the sky. One ufo made a turn towards the west, one ufo had a west-east trajectory. Uniform speed, many times greater than an average passenger airplane.5: calm, observing and accepting during observation, followed by disbelief, this was repeated ten times until it was no longer followed by disbelief. It seemed ordinary in a strange way.6: I loosed sight of the objects as they moved closer to the horizon, where they disappeared in the more white light towards the horizon. I would say they disappeared from sight due to the angle through the atmosphere I was seeing them; as they got closer to the horizon they were obscured by the increasing amount of air/humidity/pollution through which I saw them.I did not have a camera with me, and I would have needed some really expensive gear for the pictures to have been interesting at any rate, due to the speed and altitude at which they were flying.