Kiev is a beautiful city and 'the' place to please your eyes and heart!
It is one of the greenest cities on earth!
The city is the most(+) in spring-summer (lets say april-june), other times of the year are not worse ofcourse, it's just that in this period everything starts blooming!
-> The trees (chestnut trees, acacia trees, fruit trees), flowers (tulips, lilacs and lots of other flowers), etc.
There is beautiful "Botanic Garden".. especialy around May everything is in their 100%.

You can go on the river "Dniepr" by taking a steamboat where you can sit, drink/eat something, relax & enjoy the great view.
...or just hire a small boat with your friend and use your own arm-power to move and swimm around water lillies :) .

The Centre of the city "Chrechiatik", has a large shopping centre undergound - just under the "Maydan Nezalezhnosti"( Independence Squar).
(let me give you some extra info.. ->  http://images.google.com/imgres?imgurl=http://www.mapofukraine.net/kyiv/pics/maydan_nezalezhnosti.jpg&imgrefurl=http://www.mapofukraine.net/kyiv/sightseeing_of_kiev.html&h=323&w=430&sz=41&hl=en&start=1&sig2=QzKxcKFdywdhaTYt80lU4A&um=1&tbnid=Z80Gk6iq9aA9VM:&tbnh=95&tbnw=126&ei=4GgQSJrKBJqUwQHdtLyCCQ&prev=/images%3Fq%3Dmaydan%2Bnezalezhnosti%2Bkiev%26um%3D1%26hl%3Den%26sa%3DN  )