Kew Gardens
It states on the Royal Botanical Gardens at Kew website:
Our mission at Kew Gardens and Wakehurst is to understand and protect plants and fungi, for the wellbeing of people and the future of all life on Earth.
And a very good job they are doing too.
Before you even step into one of the sweaty, steamy hot houses my advice is not to drive to Kew. Parking on-site is very limited and the normal London traffic, horrendous. We travelled by coach which although less stressful, gave us only four hours to explore which is nowhere near enough. Take the train and underground and make a real day of it.
Covering 326 acres, grab a map and pick your main points of interest; there really is too much for one visit.
Personally, the temperate houses are a must, the pagoda (extra fee payable), the waterlily house (lovely), the rose garden (fragrant), the hive (interesting) and the mediterranean garden (scented).
One disappointment I thought was the tree top walk. Okay, a bit bland but do it because it's there.
Kew boasts over 50,000 plant species including the Titan Arum, one of the world's smelliest plants. Amazingly, it first flowered at Kew in 1889. If there is one plant or fungi you have always wanted to see, then Kew probably has it.
If I gave stars for places Kew would get five.