Zenkō-ji is the spiritual heart of Nagano, a Buddhist temple of such ancient standing that it predates sectarian Buddhism in Japan — it has no formal denomination and welcomes believers of every school. The temple was founded in the 7th century and the present main hall, completed in 1707, is a massive wooden structure designated a National Treasure. The stone-paved Omotesandō approach road leading up from the city centre passes between rows of traditional inn-temples called shukubo, where pilgrims have lodged for centuries, and the incense smoke from the great cauldrons at the gate hangs over the crowds regardless of the season.
The temple grounds hold several smaller halls and structures, but the main attraction for most visitors is the Okaidan tunnel, a narrow, pitch-dark passageway beneath the main hall. Visitors enter in complete darkness and feel their way along a wall-rail to touch the Sacred Key — a symbolic act of receiving the Buddha's grace. The experience is brief and genuinely disorienting, which only adds to its power. The approach and grounds are best visited early in the morning when pilgrims perform their dawn rituals; the atmosphere before the tour buses arrive is considerably more contemplative.