Nachi Primeval Forest, Sacred grove in Nachikatsuura, Japan.

Nachi Primeval Forest is a 33.5-hectare old-growth forest on the slopes of Mount Nachi, east of Nachi Falls in Nachikatsuura, Wakayama Prefecture. It belongs to Kumano Nachi Taisha shrine and mixes warm-climate broadleaf trees such as isunoki, shii and urajirogashi with temperate broadleaf and conifer species. Its understory is rich in ferns and vines, and a hortoki tree nearly 5 meters in diameter grows there.

The forest belongs to Kumano Nachi Taisha shrine and was designated a National Natural Monument on 3 March 1928. In July 2004 it was inscribed on the UNESCO World Heritage list as part of the Sacred Sites and Pilgrimage Routes in the Kii Mountain Range. Between late October 1901 and October 1904, the botanist Minakata Kumagusu collected specimens there over 6 days.

The forest belongs to Kumano Nachi Taisha shrine, and its trees stand east of Nachi Falls, the waterfall venerated at the shrine. The woodland is part of the 2004 UNESCO World Heritage Site "Sacred Sites and Pilgrimage Routes in the Kii Mountain Range", alongside the shrine and falls.

The terrain is wet and slippery year-round due to high humidity and frequent moisture, so sturdy footwear is essential for safe walking. Check conditions before visiting, especially during rainy seasons when trails become more challenging.

Minakata Kumagusu collected plant specimens in the forest over six separate stays between late October 1901 and October 1904. The woodland is also home to a large Japanese olive tree (Horutonoki) with a trunk nearly 5 metres in diameter.