Are there any places on earth completely barren with nothing on the horizon in any direction?

In Botswana the Makgadikgadi Pan qualifies, which is one of the largest salt flats in the world.

image source

Lying southeast of the Okavango Delta and surrounded by the Kalahari Desert, Makgadikgadi is technically not a single pan but many pans with sandy desert in between, the largest being the Sua (Sowa), Nwetwe and Nxai Pans. The largest individual pan is about 1,900 sq mi (4,921.0 km2). In comparison, Salar de Uyuni in Bolivia is a single salt flat of 4,100 sq mi (10,619.0 km2), rarely has much water, and is generally claimed to be the world's largest salt pan. A dry salty clay crust most of the year, the pans are seasonally covered with water and grass, and are then a refuge for birds and animals in this very arid part of the world. The climate is hot and dry but with regular annual rains.

There are places like that in Kazakhstan. Check http://welovemountains.net/cycling-east-part-18-aktau-riding-in-kazakhstan-pt1/

A lot of Saskatchewan is like that (photo from here). You can see just how flat it is from the topo maps. In some places it's yellow rapeseed (canola) to the horizons.