What to know
Iozan (硫黄山, Iōzan, meaning "Sulfur Mountain") is an active volcano near Kawayu Onsen. Its yellow sulfur vents are accessible up close, as visitors can freely walk around the steaming area. Eggs cooked by the mountain's natural heat are often sold near the vents, and more refreshments are available at the Iozan Visitor Center.
Several trails offer pleasant walks around the mountain. The longest route (2.5 km) leads to the visitor center of nearby Kawayu Onsen. This flat path goes through shrubs and low brush around Iozan before entering the forested area of Kawayu Onsen.
Iozan is located just outside the hot spring resort of Kawayu Onsen. The volcanic area is less than a five-minute drive from the town center. On foot, it takes about 45 minutes from the town center or about 20 minutes from Kawayu Onsen Station.
During certain weeks in winter (January 24 to March 1, 2026) and summer (July 26 to August 31, 2025), infrequent buses between Lake Mashu, Kawayu Station, Kawayu Onsen, and Lake Kussharo stop at Mount Iozan. No bus service operates the rest of the year.
There is a paid parking lot (500 yen) at Iozan. The parking ticket also allows parking at Observation Deck No. 1 at Lake Mashu.
How to get to and around Akan Mashu National Park
Visitor information
Practical details to check before planning this stop.
- Hours
- Closed
- Admission
- English name
- Teshikaga Eco Passport
- Original name
- Iozan (Sulfur Mountain)
Verify details before visiting. Currency conversion is indicative and may vary over time.