Parque Natural el Toa, immediately west of Parque Natural Duaba [1], extends into the interior mountains. The seven-kilometer-long Sendero Juncal Rencontra trail transcends the mountains, leading from the Río Duaba to the Río Toa; guided hikes (CUC22 from Baracoa) end with a boat or jeep return. Visits need to be coordinated with EcoTur or Gaviota.
Links:
[1] http://www.moon.com/destinations/cuba/guantanamo-province/baracoa/baracoa-excursions/parque-natural-duaba-and-el-yunque