Best way to get to Ljublana

You might strart by feeding the info into flight search engine like Skyscanner, matrix.ita, or Google flights. Note schedule and prices.

Then look at going to Venice and home from Rome. You can get a Go-Opti van from Venice to Ljubljana, and a Vueling flight to Rome. Figure to spend time in Venice and Rome. Now compare options.

Our inbound path this Summer will be:
DEN - LHR - BLQ via air. Then train from Bologna - Trieste - Ljubljana.
Why fly into Bologna? Because, for us, British Airways had better flight connections/schedule into BLQ vs VCE.

Our outbound path this Fall will be:
Train from Ljubljana to Wien.
VIE - LHR - DEN for the flight home.

Since Ljubliana is a small airport in a small city the prices to fly there from the US are considerably expensive. When we went in 2017, we flew into Venice and then rented a car to drive to Ljubliana. It saved us over $1000 per person to do it this way.

I took a GoOpti van transfer from Ljubljana to Venice in June, 2018 and it took about 3 hours between the cities. Several people in our van got out at the Venice airport, first, where there is a dedicated "GoOpti" pick-up/drop-off area. You might take a look at the GoOpti website and consider flying DC-Venice then booking a transfer from the Venice airport to Ljubljana approx. 2-3 hours after landing. Or - as suggested - stay in Venice for some time before then booking a GoOpti from Piazza Marco Polo in the main part of Venice.

Take a look at flying into Zagreb and getting a train or bus from there. The travel time may not be terribly different from what you'd have through Venice, but the cost might be lower (or not).

I'm taking this same tour starting on June 2nd. I'm flying from Seattle and last fall I found a great price on Delta from Seattle to Munich so I booked it. I'll take the train from Munich to Salzburg and spend a couple of days there. Then take the train from Salzburg to Ljubljana. I'm looking forward to the scenic train ride through the alps. It's about 4.5 hours. Going home I'm flying from Dubrovnik back to Munich and then home from there. I found a Lufthansa flight from Dubrovnik for 146.00 Euro. Unfortunately there are extra travel expenses going to a smaller town to start the tour.
Vanessa

You probably have booked your travel by now but we are also taking the Adriatic tour starting May 12. We are flying via Luftansa from Newark to Munich (9-10) then are planning on taking the train from Munich to Ljubljana on the 10th. On the way home we booked a flight from Dubrovnik to Munich then on to Newark. The tricky part for us was making sure we understood the train schedule because there are two transfers.

We are taking the Best of Eastern Europe tour in June. It goes in the opposite direction of the Adriatic tour (it ends in Bled rather than starts there). After poking around this forum and looking in the RS guidebook, I decided to take GoOpti from Ljubljana to Venice and fly home from there. The flight from Venice is a direct flight. We are in New York; I suspect that DC has similar flights to and from major cities as New York does. Layovers and changing planes are my least favorite things about travel, and I avoid them whenever I can.

I have no experience coming home from Dubrovnik. But my brother toured the Adriatic a couple of years ago and had to lay over in Paris (CDG). He overnighted at the Ibis Hotel at the airport.