Greek Islands and Eastern Europe

You have prior European travel experience, which definitely puts you ahead of the game, but the Greek islands are different, logistically. You'll be traveling by ferry or plane, both more subject to weather cancellations that trains and buses are. You don't list Athens but I assure you that you'll be spending time there (possibly more than once, depending on schedules) because it's the gateway to the islands. I think four different islands in 8 days is pretty aggressive. Although Santorini, Naxos and Milos are fairly close together--and I assume you can move between them without returning to Athens, Crete is a large island where I think (as you do more planning) you'll want more than 2 or 3 days.

Before getting too detailed in your planning for Croatia or Montenegro (both lovely), take a look at transportation from Greece. Proximity doesn't guarantee good connections. And getting back home from Montenegro might also be challenging. Especially for intra-European flights, skyscanner.com is a good resource.

Flights to Montenegro will be into the capital, Podgorica (possibly with a change in a northern city like Munich, so potentially not a fast trip and not cheap). It is not a place you want to spend much time. Fortunately, the country is small and there's decent bus service from Podgorica to other spots. I didn't get to the national parks (unless Lake Skadar is one), but I've read good things about them. Certainly the towns of Ulcinj (Turkish vibe), Cetinje, Herceg Novi, Kotor and Budva are worth seeing. And the bus trip around (or boat trip on) the Bay of Kotor is one of Europe's great sights.

I flew home from Zagreb, Croatia, with just one stop on the way to Washington-Dulles, but I haven't checked connections from Greece. I'm not an athletic traveler so have no personal recommendations for you, but in 2015 I noticed a zip line in Istria. I think it was in Pazin, which is the administrative capital of Croatian Istria. Istria is very pretty, with hills in the interior and some historic towns along the coast. It's good to have a car there, but with patience you can move around by bus.

Croatia a lot more touristy, overall, than Montenegro. Within Montenegro, Budva and Kotor seem to get the vast majority of the tourist traffic. Kotor, at least, is a destination (though not daily as of 2015) for mega-ships. It's not a great experience, being in Kotor on the day one of those monsters is in port. I assume you have the same situation in Croatia. I haven't spent time on the southern coast of Croatia recently.

If you opt for Croatia, try to make it to Plitvice Lakes National Park, which is really beautiful. The walking in the park is easy, but the surroundings are lovely. The trick at the park is that you must spend the night at or near the park before you visit so you can get an early start the next day. If you do not do that, you will be moving down the walkways with an unbelievable crowd of day-trippers.

Hello DevN2. For a Honeymoon trip, I recommend being at Greece, only.
Fly from the airport of Athens to the airport on the island Naxos. A minimum of four nights on Naxos.
Ferry boat from Naxos to Santorini. Three nights on Santorini.
Fly from Santorini to Athens airport.
Fly from Athens airport to Crete. Be at Crete seven nights.
Fly from Crete to Athens airport.
Be at Athens three nights (if you are interested in being in museums).

Just because Croatia and Montenegro look close doesn’t mean they are easy to get to. Stay in Greece.

Island hopping sounds great on a cruise or with a private boat. But if you are going by public ferry and changing hotels, 8 days (7 or 8 nights?) for 3 or 4 islands, means a string of 1- and 2-nighters and maybe a lot of time on the ferries.

Hello,

Regarding Greek Island Hopping I can surely say it is possible since I did it last summer. However, you have to be able to make your accommodation bookings earlier and of course, you must be a bit flexible. We toured the Cyclades and spend 2 nights max on each destination. It was a bit of an adventure and I enjoyed it a lot. If you go island hopping in the Cyclades, like we did, you won't spend most of your time on the ship since these islands are close to one another. I'd prefer this option to a cruise any time because we could make our own program and on a budget. I used an e-pass with the Hellenic Seaways ferries to do this. It was pretty easy to get from one island to the next, though they did allow certain schedules for the e-pass. You can check out the ferries section at Hostelbay if you like.

You could easily spend 2 and a half weeks just in Greece, and have a wonderful time. Lots of opportunities for hiking, biking and watersports. One of the most fascinating islands is Nisyros, which has an active (but not erupting) volcano that you can hike into.

If you are set on adding another country, I would suggest Turkey. You can access the west coast (Turquoise Coast) of Turkey via ferry from Rhodes.

In Turkey, you could hike the Lycean Trail, visit some archeological sites, take boat trips, make your way to Cappadocia for an incredible hot air balloon ride, then fly to Istanbul, spend a few nights and fly home from there.

There are limited ferry connections from the Cyclades islands to Rhodes. Your best bet is the reliable Blue Star line, which has an overnight ferry leaving Santorini shortly after midnight on Wednesday, Friday and Monday and arriving Rhodes at 9 am. You could ferry directly to Marmaris or spend a night on Rhodes.

So your itinerary would be: arrive Athens, fly or ferry to Naxos, ferry to Santorini, ferry to Rhodes, ferry to Marmaris, fly to Istanbul, fly home.

I absolutely support the suggestion you spend your whole vacation in Greece.

Two and a half weeks is just a comfortable time to explore three islands, four at the most. Doing four islands within 8 days is just not feasible. You'd spend more time rushing from one place to the next rather than enjoying the islands. Remember you will pretty much need a whole day for traveling each time you change locations.

My recommendation is you count the total nights (not the days!) you are going to have, and then think how many days you want to spend on each island.

Like if you have a total of 16 nights between arrival and departure, that would realistically give you three full days (= four nights) on each of those four islands you named. For a honeymoon, you would probably not want to feel rushed all the time but rather explore, relax, and enjoy, so three days is just the minimum, IMO.

My reccomendation would be (as long as you are comfortable with more temperate climates than Greece in the summer) would be stay in the Islands for 10 days and then head up North to the twin sisters of the Baltic, Helsinki and Tallinn. Two beautiful cities, each with their own unique thing to offer. I know people tend not to think of Finland as a great travel destination but you will love it!