Paraguay does not really have much to offer in terms of highlights in our opinion, especially compared to other places in South America. What we enjoyed most are the places we stayed at in Altos (Hasta la Pasta) and in the Chaco (Harmony of Wilderness, Rosaleda Resort), all of which have been established by Swiss and German immigrants.
Ciudad del Este
Ciudad del Este essentially is a big shopping mall for Brazilians. Besides that we visited the Saltos del Monday waterfalls and the Represa de Itaipú.
Asunción has a small center with a few beautiful graffiti and a handful of colonial buildings.
The Chaco is at the same time a boring yet interesting experience. All roads go in straight lines through the same monotonous landscape. It is impressive though, how the Mennonites managed to make a living in this semi-arid region starting around the 1930s. Even Paraguayans from the east looked at us with fearful eyes when we told them that we were going to the Chaco. In reality the Chaco is easy to travel and offers almost everything that you get elsewhere. It is still recommended to take plentiful of water when leaving the main roads though.