Sauce is a city in San Martin.
Shared taxi or combi from Tarapoto. In Tarapoto you need to take mototaxi to the "paradero" (station) to Sauce
Laguna Azul - many hotels give boat rides on the lake Waterfalls - there are several waterfals to see
Suace Resort - the fancy resort Puerto Azul - a very cute family-run hotel in the "2 de Mayo" village near Sauce.