Looking at the ferry schedules and private excursion outfits, there doesn't seem to be an easy and affordable way to do a day trip to Mljet National Park from Dubrovnik in late May. There are many options starting June 1 (summer season) but that won't work for our itinerary. Best option in May seems to be the car ferry from Prapratno to Sobra, departs at 7:00 AM and returns at 19:00. I guess we could take a taxi from Old Town Dubrovnik where we are staying. Does any way know of a better option?