Baltic countries and/or Belarus

Can't help you with Belarus. It seems like you need to fly in/out if you want to visit without a visa. But if you can work that out and have enough time to visit plus the other three, why not?

I visited Lithuania, Latvia, and Estonia in 2016. It's easy to visit them independently by public transportation - I did. The best mode of connection between the three capitals is long distance bus. You can use buses and trains to get between places from the three capitals. I took the train from Vilnius to Kaunas and from Riga to a few places. No doubt you can plot out the best way to get to any off-the-map places you might be considering. Try Google Maps and Rome2Rio.

I took "free" walking tours in Riga and Tallinn.

FYI, at the end of my Baltics trip, I tacked on a ferry trip from Helsinki to St. Petersburg and back for three days, which you can do without a visa if you go by ferry for up to 72 hours. It was really a lot of fun. But that might be outside the scope of your trip.

Likewise, can't help you (yet) with Belarus.

I visited Lithuania, Latvia and Estonia last summer (June-July 2018). I spent about 2 and a half weeks there, rented a car and went off the main tourist circuit (as best I can tell, almost all foreign tourists stick entirely to the three capitols). I loved all three countries, each was unique, full of worthwhile things, and we found completely fascinating places and things both in the big cities, and way out in the hinterlands.

We rented a car in Vilnius and returned it in Tallinn a couple weeks later after driving all over. It was one of the best trips I've done to date, it far exceeded my expectations, and I felt like could have spent a lot more time exploring and would not have run out of things to do/see. Travel there is easy, not expensive, and full of delightful surprises. Not much of a language barrier (IME that's 100% generational: if you see someone with gray hair, they will want to speak Russian, not English; anyone without gray hair will happily speak perfect, unaccented English as well as you do).

By all means, if you go, don't feel like you need to stick to the Tallin-Riga-Vilnius axis - there's plenty of great stuff beyond the major cities. So much history there. We really enjoyed all of Latvia (we went from the far west to east of Riga - did not get all the way to the eastern border with Belarus, but everywhere we went we found interesting things).

No need for a private guide. We went everywhere and it was about as easy as travel in Spain, Italy or anywhere else.

I spent two weeks in the three capitals in the summer of 2017. There's plenty see there. If you search for the city names in the trip reports section, you can find my narrations for each stay. There is plenty to do in those cities--but we're already talking about returning to see places we couldn't fit in.

The Baltics have a very good system of private bus lines that run between cities. If you don't want to drive, that is a good choice. We did that between Tallinn and Riga, and it worked out well.

I visited Belarus this summer on the 5 day visa that one can obtain on arrival. Visa was free - one only needs to purchase the travel insurance ($7 for 5 days) at the desk prior to approaching the immigration desk. The new visa is only available if flying into Minsk and cannot be obtained when crossing a land border. While we were in Belarus, the gov't changed it from 5 days to 30 days for the free visa.

We spent a couple of days in Minsk and then hired a car (100 euros for 4 of us) to drive us to Mir and Nesvizh castles and after that got dropped at the Branovichi train station rather than back track to Minsk. Then took the train to Brest for 1 night - visited the fortress and the downtown area. Next day returned to Minsk and flew to Odessa the next day.

While in Minsk did a free walking tour of the downtown area and also did a paid tour of the Jewish areas of Minsk. In Minsk, traveled around using Uber though automatic payments with credit cards didn't work.

Let me know if you have other questions.

Is the above a good enough excuse to travel somewhere?

From my perspective, any reason is a good enough excuse to travel. I traveled to Tallinn and Riga this summer for 7 days primarily because I wanted to fly on an Airbus A350-900. I found a cheap business class ticket into Tallinn and out of Riga. Bonus: I got to fly on a new airline (Air Baltic) and got to fly on 2 other new planes to me (CS300 and Q400). I'm a Cold War history buff, so the destinations were not totally random. By the way, I loved both places. I also took a couple of day trips outside the capitols and would love to go back to spend more time doing something more like what David described above.

I leave for Germany on Thursday. Primary reason? To see a German band I like play a couple of live shows. Is that a good enough excuse to travel somewhere? For me, yes!

We traveled to Belarus on our own to visit my husband’s Jewish grandparents’ birthplaces. We did the whole trip on our own. It took quite a bit of planning, but turned out to be one of our most memorable trips. We went before the airport visas, and got a 30 day visa from the consulate in DC. We even rented a car, since the birthplaces were quite spread out. If you decide to go, send me a private message and I can dig up some more specific tips.

Visa rules for Belarus are changing quite quickly. If you go there have the latest information. In Baltic republics English is widely spoken and understood, not so in Belarus. "is the above a good enough excuse to travel somewhere?" How can I answer? I go somewhere because I want. I don't need excuses.