La Cabaña is one of Asuncion's most established steak restaurants — a proper parrilla with an open grill visible from the dining room and a menu built around cuts of Paraguayan beef that hold their own against anything you'll find in Argentina or Uruguay. The beef ribs (costillas) and entrecôte are reliably good; the chimichurri is made in-house.
The atmosphere is old-fashioned in the best sense — white tablecloths, attentive service, a wine list that actually includes some decent South American options. It is not cheap by Paraguayan standards, but it is not expensive by any international measure. Reservations are worth making at weekends.