Trebinje is just 30km north of Dubrovnik and most travellers arrive from there. The drive is spectacular — up the Adriatic karst and over the mountains via the Ivanica or Brgat border crossings — and takes about 45 minutes without queues. Bus services run daily between Dubrovnik and Trebinje (about €10, 90 minutes including the border).
From elsewhere in Bosnia, Trebinje is at the southern end of a long, slow road from Mostar (two hours, gorgeous scenery) or Sarajevo (five to six hours via Foča). The closest airport is Dubrovnik (DBV); Mostar (OMO) and Tivat (TIV) in Montenegro are alternatives.