Rurrenabaque is a small town on the Río Beni where the last ridge of the Andes gives out and the Amazon basin begins. It is hot, low and green, and it exists for visitors in a way the rest of the Beni does not: a few streets of guesthouses and agencies between the river and the airstrip.
The flight from La Paz takes under an hour and crosses the whole Cordillera; the bus takes eighteen and is the reason most people fly. Both are weather-dependent, and the airstrip closes when it rains hard.
Two trips leave from here and they are not interchangeable. The pampas, up the Río Yacuma about three hours by road and then by boat, are flooded savannah where the wildlife is concentrated at the water's edge and easy to see — caiman, capybara, turtles, and pink river dolphins that will swim alongside the boat. The jungle means Madidi National Park, upriver, where the forest is denser and you will see far less and it will matter far more. Madidi runs from 200 to 6,000 metres and is among the most biodiverse protected areas on the planet.
The good lodges inside Madidi are community-owned, which is unusual and deliberate: San José de Uchupiamonas has run Chalalán since the 1990s, and the money stays in the village rather than in La Paz.
Go between May and October if you can. The wet season is genuinely wet.