Kawah Ijen, Indonesia
This hike takes you via a steep two-mile trail up to the ethereal blue-green crater lake of Kawah Ijen, taking two hours total. The trail is usually carried out just before dawn in hopes of catching the unique blue flame over the crater's sulfur deposits. This is suitable for anyone of moderate fitness but should only be carried out during peak months between April and October. It can be wet and slippery outside of this period. It's recommended that you go with a guide for this tour as you'll be hiking in the dark and will also need to wear a gas mask when close to the lake due to the sulphuric gas. To get there, you will need to fly to Denpasar Airport in Bali, then take a ferry over to Java Island, which drops you directly in Banyuwangi for pickup by your guide. There are also limited flights directly to Blimbingsari Airport.