Start with the 07:11 İDO ferry from Istanbul to Yalova, about 1h 10m. Transfer in Yalova, then take the 11:15 FlixBus bus on to Orhangazi (15 min). Transfer in Orhangazi, then take the 13:00 FlixBus bus on to İstanbul Esenler (2h 45m). Transfer in İstanbul Esenler, then take the 17:45 (+1d) FlixBus bus on to Sofia (8h 30m). You arrive in Sofia around 02:15 (+1d). In total it's roughly EUR 90 over 20h 15m, 3 transfers.
İDO
FlixBusOpens Omio — enter your date to compare trains and buses for this route; the price is finalised at checkout.
FlixBusOpens Omio — enter your date to compare trains and buses for this route; the price is finalised at checkout.
FlixBusOpens Omio — enter your date to compare trains and buses for this route; the price is finalised at checkout.
Ground-only route to Sofia by ferry + bus. Ferry (İDO, 1h 10min) + Bus (FlixBus, 15min) via Yalova + Bus (FlixBus, 2h 45min) via Orhangazi + Bus (FlixBus, 8h 30min) via İstanbul Esenler.