Look to Windward
by Iain M Banks
One of the easier to read culture novels. Told in an intersting way and without a predictable outcome whilst reading it, nor a clear answer to who did (or didn't) do it. What continues to impress is the way Iain M Banks is able to really drill home timeless infinity that defines our galaxy and the universe beyond it.
The culture, whilst one of the more advanced and expansive civilisations in the galaxy, are portrayed as really just in their mid-20s. Very clever and important, but really not quite able to compete with those even more advanced.