Cenote Noolha is a cave cenote about two kilometres north of Valladolid's main plaza. Stairs lead down to a wooden deck beside the water, where you can swim in clear, deep water and see shafts of sun reach into the cave.
It is more built up than some rural cenotes, with life jackets, showers, a snack bar, hammocks, jumping boards, and a zipline. Go early if you want a quieter swim, as tour groups tend to arrive later in the morning.