Building a new capital from scratch, often results in a large and consistent set of period architecture. Fatehpur Sikri or Jaipur come to my mind. A capital needs many buildings. You need offices for the government, you need more residential areas for the influx of inhabitants and you need to provide public services. And more likely than not, you will build using the at the time hip architectural style. Kaunas is no different.
After WW 1, the Polish occupied the main city of Lithuania: Vilnius. The temporary capital of the new found country of Lithuania was established in Kaunus. The original historic town was greatly enlarged by new, modernist buildings. They went all in and the amount and consistency of the modernist buildings is unique.
OUV
I feel the modernist architecture is unique and consistent enough to warrant inscription. It's not backward looking, but represents cutting edge architecture of the time.
Getting There
Kaunas lies on the main highway between Vilnius and Klaipeda (Curonian Split). It's a natural stop, if you travel from Vilnius to the coast and plan to tick off all sites in Lithuania In the city, I did everything on foot.