Grutas Los Herrera is the easy natural counterweight to the Ranas ruins. The cave route leads through chambers of stalactites and stalagmites, with enough lighting and paths to make it accessible without turning it into a theme-park cave.
It is close to town, so it works well as part of a half-day loop with Ranas or Campo Alegre. Bring a light layer; the mountain air is already cooler than Querétaro city, and the cave is cooler still.