The fold on the map

Why is always the place to be located in the fold on the map? We have four weeks of freedom (=vacation). We are planning a short trip to Sigtuna, the first capital of Sweden. I have never been there. The old town is said to be beautiful.

My fatigue prevents me from doing some effort now, but planning a little trip I can do. And hopefully I will be good soon, so I can go on the trip.