I visited this WHS in April 2017. I visited all 3 locations over 4 days, namely the Manjanggul Lava Tube from the Geomunoreum Lava Tube System, Mt Hallasan and Seongsan Ilchulbong Tuff Cone. All entrances have free admission in April.

The only lava tube open to tourists is the Manjanggul Lava Tube which is 7.4km long, 18m wide and 23m high. Only 1 km is accessible but it is more than enough to grasp the OUV of this unique lava tube. The vast majority of lava tubes are formed by a basaltic lava flow which contains less viscosity. When the lava flow from the volcanic crater stops, it forms an empty space shaped like a tube. Thenm the lava flows continuously into this tube, the ground melts down in the high temperature and deepens gradually.

A number of impressive lava formations can be observed while walking underground for 1km: lava flowstones, lava rafts, lava shelves, lava stalactites and stalagmites, lava flowlines, quartzite fragments and last but certainly not least, the world's largest known 7.6m high lava column (picture, top right). The small information centre has a number of information boards and lava fragments as well as the original UNESCO certificate (picture, top left).

The second location I visited was Mt Hallasan. This is where a rental car comes in handy as I managed to drive through the never-ending maze of green tea plantations (not the ones at O'Sulloc; picture, bottom left) beneath Mt Hallasan. The mountain peak is also visible from Yongmeori or from Jungmun.

The third location I visited was the Sunrise Peak tuff cone. As the name suggests, the views at sunrise (on a clear day) are incredible (picture, bottom right). Here I could clearly experience the unequalled quality of scenic value (criterion vii) and the world class geological value (criterion viii) of this WHS. The 180m climb to the top of the tuff cone is very worthwhile but if you wait around 30 minutes after sunrise, you'll be rewarded with similar views but without the crowds. The tuff cone is also visible from the Phoenix Island Resort as well as from U-do island. If you have time to spare, there are several short hikes to the black sandy beaches beneath the tuff cone.

Overall, I enjoyed my time in Jeju. The island proudly displays its 3 titles, namely UNESCO world natural heritage, part of the Glocal Geoparks Network and 1 of the 7 wonders of nature however you'll need a significant dose of patience and time to take in the 3 locations before the bus loads of Chinese and Korean tourists. I'd recommend a visit to the Yongmeori Coast as well as U-do island by ferry (possible future extension).