One of the most incredible and surreal places I've been to. After a rocky jeep ride and a long hike with stunning views (encountering the Ijen sulphur miners en route) you come to the surreal landscape of Lake Ijen, a sulphuric acid lake of turquoise blue (and a foul stench) where miners work for under $10 a day and for a pack of cigarettes you can take a photo of them as they carry their heavy bright yellow load with just a straw basket. Spectacular landscape and a world away from usual Javan landscapes.
East Java near Randu Agung.
Google map: bit.ly/SSuxwZ