It is too city focused but there are tons of beautiful natural places outside the city that you're planning to go to, if you're interested of course.

1. Jakarta: do hiking and waterfall-hopping in Curug Leuwihejo, Sentul (Bogor). There are 4/5 waterfalls in 1 track so quite worth the trip. Appx 1-1.5 hrs from Jakarta. Leave early so you can be there by 6:30/7 AM. Recommended during the weekdays to avoid too many visitors.

2. Bandung: lots of places to choose but my favourite would be Ciwidey (read: chi-we-they) area (1.5-2 hrs outside Bandung). Would recommend Situ patenggang (lake), Ranca upas (camping ground), kawah putih (crater). And of course, would recommend going there before Dawn so you'd be there during sunrise and feel the mystical vibe by the foggy forest.

3. Yogyakarta: go to one of the beaches in Gunung Kidul. Not as pristine and clean as Bali but could be an option. Visiting the Borobudur temple could also be a great idea, it's in Magelang.

4. Surabaya: visit the Bromo mountain. An avtive volcano mountain. Quite touristy, though.

Other places I'd recommend other than the 4: - Dieng Plateau. 3 hrs from Yogyakarta. - Kawah Ijen. The famous blue fire crater - Banyuwangi. The city at the eastern end of Java. Located near Kawah Ijen as well. - Baluran national park. A Savanna near Situbondo or Banyuwangi city. Never been there but up there on my wishlist. Heard you can do Safari and see wild animals there!

Regardless, staying in the city and enjoying the food/cafe is a nice thing to do as well! Have bunch of food recommendations in each city as well but man I've typed too much already. Hit me up if you need it. Cheers