Eastern Java is a great region of Indonesia to explore, especially combining a stay at Yogyakarta in Central Java with Bali to the East.
Travelling through this region will reveal stunning volcanoes such as Mount Bromo and the dramatic landscapes of Ijen on the far eastern tip of Java, with Bali in sight.
The urban sprawl of Surabaya has little to detain most visitors although Malang by contrast is cooler, cleaner, more manageable and has some interesting sights.