Literally: harbor – harbor – bay – bay
Alternately: Everywhere; every inch of the country; throughout the entire land (of Japan).
Notes: Naturally, this can also be written with the repetition mark, as 津々浦々.
This compound is somewhat unusual in that it uses only the native Japanese pronunciations of the characters (so-called kun readings); many compounds and many yojijukugo keep things short by using Chinese-derived pronunciations (on readings). The emphasis derived from doubling each character functions as a sort of plural in a language that technically has no systematic grammatical plural.
This compound is contrasting human-shaped ports and natural seaside. But the combination of littoral features coming to mean “everything in the whole country” goes to show how much Japanese culture has traditionally been one of open lowlands and the sea, rather than the forested mountains that make up so much of the archipelago’s land area.