Irohazaka (いろは坂) is a pair of winding roads that connect the lower elevations near central Nikko to the higher elevations of the mountainous Okunikko region. "Iroha" are the first three of 48 syllables of the formerly used Japanese alphabet (which is now known as "aiueo"), and "zaka" means "slope" - the Irohazaka Winding Roads were so named because together they consist of 48 hairpin turns.
The two roads were respectively built in 1954 and 1965 as some of Japan's first toll roads, but were later turned toll free. Today, the older road is only open to downward traffic and includes a pit stop from where you can see two waterfalls. The newer road, meanwhile, is only open to upward traffic as far as the Akechidaira Plateau near the top of the road. The plateau offers an observation deck with views over the Irohazaka and the valley below.
Spectacular autumn colors along Irohazaka can usually be enjoyed from late October to early November. Due to the autumnal popularity of Nikko, traffic can get very bad along the Irohazaka, causing delays to both cars and buses. Visitors are advised to avoid weekends and national holidays and to try to go as early as possible.