Loma Plata is the oldest of the three Mennonite colony towns and the one that still looks like a working co-operative rather than a small city, and everything a visitor can book here goes through the Cooperativa Chortitzer. The standard circuit is a talk, the Heimatmuseum Colonia Menno and the Lácteos Trébol plant — the dairy whose products you have already eaten if you have eaten anything in Paraguay — with a guide, for Gs 200.000 and a maximum of 45 people. They will also put together institutional visits to the co-operative's other industries, and supply historical guiding.
What takes you further out is Laguna Capitán, 50 km east: a salt lagoon and private reserve with a campamento that has air-conditioned rooms, a parrilla, Mennonite and Paraguayan cooking, and a model dairy where you can stand in on the milking. For anyone here for the Chaco's birds rather than its history, this is the base. Beyond it, Campo María is another salt lagoon 80 km out with a viewing platform, and Fortín Isla Poí is a Chaco War position nearby.
Loma Plata pairs with Filadelfia 20 km away rather than competing with it; the Fernheim tourist office over there (entered above) and this desk cover different museums and different reserves, and between them they are the whole supply in the central Chaco.
One warning, and it is not about them: their website has been unreachable to every tool I have since at least September 2024, so the numbers above are from an April 2024 capture. Ring before you rely on them.