You can find many solutions to get across the country from Karimunjawa to Malang… they usually’re all a bit of a headache. Individually, I took a ferry from Karimunjawa to Jepara, a shared taxi from Jepara to Semarang Bus Station, a local bus from Semarang to Surabaya, annnnddd ultimately (following staying overnight and possessing a lie-in), a