Exploring Poland and the Baltic States. Any suggestions?

Exploring Northern Europe: A Journey Through Poland and the Baltic States

Embarking on a trip through northeastern Europe offers a captivating blend of history, culture, and scenic landscapes. My wife and I have recently decided to venture into this lesser-explored region, and as someone with a particular fondness for Poland, I am eager to deepen my understanding of this fascinating country. However, I must admit my knowledge is somewhat limited beyond its most well-known cities, Warsaw and Kraków.

In planning this adventure, I am seeking recommendations on must-visit destinations within Poland that lie outside the typical tourist hotspots. Are there hidden gems or culturally rich towns that should not be missed?

Transportation is also a key consideration. I am contemplating renting a car upon arrival, which would provide flexibility for exploring at our own pace. However, I am curious about the logistics: would rental agencies permit cross-border travel into neighboring Baltic countries such as Lithuania, Latvia, and Estonia? If so, what are the best practices for international car rentals, and are there any restrictions or additional fees to consider?

Given that we are aiming for a comprehensive yet manageable itinerary, I am wondering if a two-week timeframe would suffice to explore 2-3 Polish cities along with the capitals of Lithuania, Latvia, and Estonia. My plan is to be the sole driver, so I would appreciate insights into whether this amount of travel is feasible without leading to exhaustion from lengthy drives.

Any advice, personal experiences, or suggestions from fellow travelers would be immensely helpful as we prepare for this exciting journey. Thank you in advance for your insights!