There are some pretty incredible gardens in every area of the world. The use of nature to calm our nervous system and regain hope in humanity is one of the best practices there is.
No matter what city you're in, a dedicated garden, or if you're lucky, a Botanical Garden will be available. Most botanical garden have a butterfly sanctuary. This is somewhere i could spend all day in. I've seen art displays made from fake flamingos and space ships made from Christmas lights all at Botanical gardens. Most Botanical gardens are very affordable and completely worth the entrance fee.
You can find native and foreign plants, produce, and animals at a Botanical garden. I have never been to a garden that didn't have a cafe where you could find caffeine and a quick bite to eat. I've never regretted searching for an spending time a Botanical Garden.