Also they named Turku just Åbo.

Åbo.

Swedish "å" is an entire word meaning;

a river, a creek, a big stream

"Bo"

bo n

**a dwelling** (of an animal), especially a bird's nest

    fågelbo

        bird’s nest

    att bygga bo

        to build a nest / to nest ("build nest" – idiomatic phrasing)

(poetic, extended from sense 1) **a home**

sätta bo

    settle down

So it's a three letter word basically saying river-dwelling

I think rather than ask Finns what a place was named they just named them themselves. Perhaps because they were tired of the locals calling everything shit and piss. ¯\_(ツ)_/¯