Lahuen Ñadi Natural Monument, Natural monument in Llanquihue Province, Chile.

Lahuen Ñadi Natural Monument is a protected forest area located between Puerto Montt and Puerto Varas in southern Chile's Los Lagos Region. The site preserves old-growth woodland with tree species typical of the region's humid temperate environment.

Lahuen Ñadi was declared a natural monument in 2000 and is administered by CONAF, Chile's National Forest Corporation. The 200-hectare site protects the last relict alerce (Fitzroya) stands of Chile's Central Valley, some individual trees reaching 1800 years of age. Since 2015 a dispute with the Lagunitas condominium over the access road has restricted entry.

The name Lahuen Ñadi combines the Mapudungun words for 'place of alerces' and the waterlogged volcanic soil called ñadi. The two trails are named after birds: Los Chucaos for the chucao tapaculo and Los Carpinteros for the woodpeckers heard in the older stands.

Access is from the Lagunitas condominium entrance on Route 226 toward El Tepual airport, then about 3 km north along the El Rincón property road. A 2016 dispute over this road keeps entry restricted, so visitors may enter only with park rangers or in residents' vehicles; contact CONAF Puerto Montt beforehand. The 600 m Los Chucaos loop is a universal-access boardwalk with public and universal restrooms at its start.

The name ñadi refers to the waterlogged volcanic soils the forest grows on, and the Mapudungun word Lahuen means a place of abundant birdsong. The 600-metre Los Chucaos trail is built as a universal-access boardwalk with public and universal toilets at its start, and it leads to an alerce estimated at 1800 years old.