That building on the mountain is a church known as Santa Cova de Montserrat. What's impressive is that it's only accessible by trail. Also, it's very near the Abbey of Montserrat in the Catalonian region of Spain. When I took this photo, I was standing not far from the abbey on an overlook near the top of Montserrat. To get up the mountain, we had to drive a precariously steep and winding road.
The landscape here is extreme and, try as I do, still can't imagine how places such as this get built. The construction must take many generations. Projects like this are not something we are likely to see again.
The Abbey of Montserrat is just an hour from Barcelona, and you can see the outskirts of the city in the distance. We didn't plan it right and arrived in the afternoon which meant we only had a couple of hours to explore. But now that we know, next time we'll spend the day exploring much more of this unbelievable monastery in the mountains.