Lake Toba on Sumatra is simply impressive because of it´s mere size and history. Approx. 75000 years ago the super-volcano erupted and almost wiped out the complete world´s population. What remains now is a huge, deep lake with an island the size of Singapore. There are a few really nice hotels on the island...
Lake Toba looks amazing from the sky, for example on Google maps...
Bali, the Indonesian vacation island east of Java is known for Hindu temples, beaches, rice fields, hotels in any budget category and great food. Temples not only include the well-known Besaki and Tanah Lot temples, but also the many home and village temples.
Jakarta is capital of the largest economy in South East Asia. More than 10 million people call the city home while the wider metropolitan area is home to 35 million. It is not really an touristic city of international status, but an important stop-over for all of Indonesia.
Mount Bromo is a volcano on Eastern Java. Even though it is active and always steaming, it is possible to walk up, to the rim of the volcano. More volcanoes are visible in the direct vicinity.
Ubud is one of the touristic centres of Bali. The busy little place features fancy hotels as well as simple cottages, rice fields and a lot of art.
Yogyakarta is a very pleasant Indonesian city. Most tourists like the city with its nice buildings, markets and wide variety of souvenirs. Nearby are several volcanos as well as the famous (Buddhist) Borobodur temple (UNESCO heritage) and Prambanan temples.