Getting there by air
The Huasteca has its own small airport at Tamuín (TQS), about 20 minutes east of Ciudad Valles, but service is thin, mostly a handful of domestic connections through Mexico City, and fares can be steep for how short the hop is. Check the schedule before you build a plan around it. Most travelers instead fly into one of the bigger gateways and drive in: San Luis Potosi city (SLP) to the west, or Tampico (TAM) on the coast to the east. Both put you roughly 4 to 5 hours from Ciudad Valles (approximate).
Getting there by road
Ciudad Valles is the natural entry point from every direction. Reckon on roughly 4 to 5 hours from San Luis Potosi city over the winding Sierra Madre climb, a similar 4 to 5 hours from Tampico across flatter ground, and a long 9 to 10 hours from Mexico City (all approximate, and the mountain sections drag). Xilitla is another 1.5 hours south of Valles up into the coffee hills.
First-class buses reach both towns and are comfortable. ADO and Vencedor run into Ciudad Valles from Mexico City’s TAPO and northern terminals; from San Luis Potosi city, Vencedor and Flecha Amarilla / regional lines make the crossing. A one-way seat from Mexico City runs somewhere around 700 to 1,100 MXN depending on class and how far ahead you book (approximate). The honest limitation: buses drop you in the towns, not at the rivers.
Getting around locally
Here is what a local would tell you straight, you want your own wheels. The falls and rivers are scattered across a wide area with almost no useful public transport linking them, and every tour meeting point assumes you can already get to a town. A rental car or a hired driver-guide for the day is the difference between seeing three sites and seeing one. Rentals are easiest arranged in San Luis Potosi city or Tampico before you arrive, since Ciudad Valles has fewer counters.
Roads to the main attractions are mostly paved but narrow and twisting, with rough dirt final stretches near some rivers (the approach to the Tamul boat launch at Tanchachín, for instance). Drive them in daylight only. After dark you get fog on the sierra, unlit curves, and livestock wandering the road, none of it worth the risk. Fill the tank in Valles or Xilitla; stations thin out fast between towns.
Colectivos and local vans connect the bigger towns (Valles to Aquismón, Valles to Xilitla) cheaply, but they run on their own loose timetable and stop early. Taxis exist in the towns; app-based rides are unreliable out here, so agree the fare before you get in.
For many people the cleanest solution is a day tour out of Ciudad Valles that bundles transport, the ejido entry and boat fees, and a guide. For Tamul specifically, where you need a boat and a guide anyway, that is often the easiest call rather than self-driving to the launch and negotiating a panga on arrival.
A note on comfort
The sierra road between San Luis Potosi city and Valles is genuinely twisty, so if anyone in the group gets carsick, sit them up front and bring something for it. Once you are down in the lowlands the driving eases, but the heat and humidity are real, keep water in the car. See the site-by-site fees and timing in visiting info.