If You are in Kiev especially during spring make sure You visit the Botanic Garden. There are a number of them but the one I visited was the Central Botanic Garden.
There, along with lots of kinds of trees and flowers, there is a very nice collection of butterflies. And if You go there in May like I did, You can see most of the flowers at their peak of beauty.
A quiet oasis in the city centre, join the local workers on their lunch break or find a shady bench amongst the greenery at any time, a lovely place to spend some time.