The "path" at the top of the steps up to Mount Bromo is only about 1 metre wide and in places the drop into the crater is sheer and considerable. Be careful, make sure you have a flashlight for any pre-dawn climb and always have your wits about you. The steps can be covered with crater dust and its possible to slip while climbing, be wary while climbing.
Bromo is an active volcano, and Semeru is a very active volcano. In June 2004, two tourists were killed at Bromo by rocks flung from a sudden explosion. The Smithsonian Institute's Volcanic Activity Report (http://www.volcano.si.edu...) keeps an eye on both, and is worth checking.
It gets very cold up on the high tops at night, probably colder than anywhere in Indonesia outside of the glacial highlands of Papua. Be suitably prepared for nightime temperatures not far above zero.
Temperatures on Mount Bromo are refreshingly cool during the day although sunburn is still a real danger, but outright cold at night, as temperatures can drop to zero in the summer and are rarely much above 5°C in winter. Some of the cheaper places to stay may not provide adequate blankets or heating, so come prepared. If needed, you can rent jackets and hats at Cemoro Lawang and at the Penanjakan viewpoint for about Rp 20,000. Hats and gloves are important if you wish to survive in the cold especially early in the morning, face masks would keep the dust away if the crowd gets big around the crater.
There are cases of malaria each year in the lower foothills of the park and any visitor planning a long stay or to camp in this area should take necessary precautions. This is not though a problem for those visiting Mount Bromo or the high plateau only.
fees/permits
To enter the park an official Rp 50,000 permit must be purchased at one of the four entrance gates.
If you intend to climb Mount Semeru only for serious trekkers and often closed due to eruptive activity you will need to apply for a permit in advance to:
Office of Bromo Tengger Semeru National Park, Jl. Raden Intan No6, PO Box 54, Malang, East Java, Indonesia. Tel: +62 341 491828