The Ybytyruzú is a 40 km ridge of forested sandstone hills east of Villarrica, protected since 1990 as a 30,000-hectare managed-resources reserve. In a country that is essentially flat, this counts as mountains, and Paraguayans treat it accordingly.
Cerro Tres Kandú, 842 m, is the highest point in Paraguay. The walk up from the Melgarejo side takes two to three hours and is steep rather than technical; local guides run it and are worth taking, because the trail forks repeatedly through private land. The view from the top is most of Guairá.
Salto Suizo is the country's highest waterfall at 62 m, dropping into a bamboo-choked gorge about 9 km from Colonia Independencia down a track that is fine in the dry and unpleasant otherwise. Smaller falls and swimming pools are scattered along the Takuara stream.
Colonia Independencia is the base most people use: a German-settled village with vineyards, a winery or two, beer and pork on the menus, and the only real tourist infrastructure in the range. The combination — Guaraní place names, German food, subtropical bamboo forest — is one of the odder things in Paraguay and entirely characteristic of it.
Go in the dry season for the tracks; go after rain for the waterfall. You cannot have both.