Oh the trees!!! There are many street trees in Vienna. A lot are ginkgos and some sort of acer and linden. Many I don't recognise at all!
I had read of a building with trees on the roof and did manage to track down the Hundertwasserhaus. Not sure all the trees were completely happy, but it was exciting to see nonetheless.
Then I walked to a large park in the east of the city. Yep, more bark to obsess over,

But the real excitement was seeing red squirrels!
No surprise what attracted them.
I sat under an oak, one of three growing together, with my feet resting up on the tree (to assist circulation after the flight). Another squirrel came down to inspect my shoes, but fled when I moved.
As I lay there, I had something of a revelation. The blessing of life is not wanting to do anything other than to be right here right now. That is enlightenment: to choose what is here and now.

A hoverfly seemed to embody it.
And with that deep sense of at-one-ness, the world is unveiled and its wonder sparkles from everywhere around.
From where I lay, I could see this...
Ah... is not that wonder in cellulose?
The following day, I went to the botanical gardens. More squirrels, more trees.
Here, again, I was blissfully happy. To meet the trees, to reside along-with the rodents and corvids for a while. To be grounded in the this-ness of here and now.
Those black poplars are impressive. Love the bark patterns of trees and the way those squirrels flow/ glide along as they run. And good paintings. Glad you enjoyed Vienna.