Sempu island is a sanctuary and best known - if already known - for its pristine blue lagoon. At Sendang Biru village one takes a traditional boat to reach the island. It happens that this village is an interesting fishermen village, which is worth your visit.
Mt. Bromo is one of Indonesia's most breathtaking sights. It's moonlike landscape, overshadowed by the highest Mt. of Java is visited often. Mt. Ijen is Javanese for ‘Lonely Mountain’ - contains the most acidic lake in the world - is far less visited.
Java's highest peak is Mt. Semeru - 3676 m. This pretty volcano can be climbed between mid April till the end of the year. It might vary a bit, as it depends on the announcements of the Park's board. During raining season the park is "rehabilitating".
The Ijen crater lake is the greatest acidic lake on earth and houses the largest blue fire area in the world. Blue fire exist during day and night, but can only be seen at night. Don't mistake Ijen's blue fire for lava, as the blue glow is the light from burning of sulphuric gases.