Oxford Botanical Garden is fantastic. Both the systematic gardens with beds containing plants from a specific family, a specific area or plants that cure a specifies illness. Other parts are dominated by colorful flowers and great looking beds. A slideshow with more photos.  I visited in 2016.

Here are several greenhouses.

Some right next to the canal.

Walled garden.

Ponds and swamp plants from around the world.

The rockery is magnificent!

The houses are pristine maintained.

The cacti house.

Only a few caudiciforms though.

The carnivorous plant have their own house.

The house with a tropical swamp.

Fern house; great floor!

Alpine house.