Kew Gardens, London

The area started as royal estates and gardens in the 1200s. Throughout the reigns of various kings and queens, land was acquired, more gardens built, buildings rose and fell, and in the 1700s the estates were merged into a large botanical garden. In the 1840s, it was formally declared the royal botanical gardens (which today means while it 'belongs' to the monarch, it's really a treasure of the state).

The gardens are used not only to collect, but to test and verify transplanted species from around the world (to break the monopoly those places had on these plants, like rubber and spices). This proved a very important economic factor as wars for over 100 years were fought over unique plant environments by the English, which is quite costly.

In the past, it fell into disrepair but the last few decades have seen a very concerted effort of conservation and upkeep that has it at an amazing state.

The Arrival - Kew Gardens Station

I took the District Line (you can also take the Overground train line) to Kew Gardens Station, which is a good hike from the gardens, but the closest you can get.

There is a little market area around the station which has a very comforting Victorian style.

Once you get there, the line to get in is crazy, but you can prepurchase your tickets online.

The Grounds

Being geared toward plants, you'll spend most of your time outside and it's a massive amount of land to cover. There are open air trams to drive you around, but I walk to try to lose some of this traveler's fat I get from drinks and sitting on planes all the time.
While this used to be a greenhouse, it is now primarily used for weddings and by extension growing one's family Kew Palace, the home of King George III, who was basically held prisoner here as he went mad The garden of the Kew Palace, much more practical plantings than I imagine they'd have back in the 1780s
Roses at the end of the season, still blooming but apparently not feeling very happy The temperate house (think ferns), the largest glass building in the world The river Thames runs along the edge of the gardens for a considerable distance
A place to dine across the pond near the Palm house.  Very serene A massive oak tree way over 100 years old and survivor of many things in the history of England
There are also a few places to eat, but I picked the Orangery, which used to house citrus plants for delicate fruit. Now it's a delightful place to get lunch and there were many options that a picky eater such as myself finds rare in the "fancy" dining establishments usually at nicer visitation spots.
Lots of options, the sandwiches were very satisfying Wine with lunch is as common as soft drinks in the United States, and kinda nice in a flora setting

Inside buildings

There are plants that even gulf stream fed England cannot support outside, and they have particular buildings to provide the environment required by the plants in them. The Lily house is one I did not go in, but the Palm House and the Temperate House were both pretty nice to wander though.
The Palm House, so so humid, it took 10 minutes for my camera to adjust and not be fogged over See, ferns in the Temperate House A Japanese art display among many other things during the Japanese Festival
Chrysanthemums, the symbol of the Emperor of Japan

Summary

Kew Gardens boasts the largest collection of plants in the world, the oldest wrought iron glass house and the largest glass house in the world, a large array of places to eat, have tea, and relax. Visiting is an entire day affair.

And of course there's a gift shop with tons of horticultural items and some other things that have me scratching my head.