The best, and sometimes only, way to visit the natural attractions around Tumbes [1] is with a travel agency. Prices are per person based on groups of two or more. The main tours are the mangrove swamps (US$25–35 pp), day trips to Amotape or the Zona Reservada (US$50–70 pp), and a day tour that includes nearby mud baths, beaches, and archaeological sites (US$25–35 pp).
The well-informed Tumbes Tours is the only Tumbes [1]-based agency (Tumbes 341, tel. 072/52-6086, www.tumbestours.com [2], 8 a.m.–1 p.m. and 2–7:30 p.m. Mon.–Sat.), otherwise you should consider one of the Máncora agencies [3].
Links:
[1] http://www.moon.com/destinations/peru/trujillo-and-the-north-coast/the-northern-beaches/tumbes
[2] http://www.tumbestours.com
[3] http://www.moon.com/destinations/peru/trujillo-and-the-north-coast/the-northern-beaches/las-pocitas