If you climb from Neptune's Nursery up to the last level of the Boboli Gardens with the statue of Abundance by Giambologna, you've reached the highest part of the park. It's called the Knight's Garden because the "Knight's Casino" was built here in the 1700s.
The three rooms of the Knight's Casino are now home to the Porcelain Museum, with a collection of objects from all of the European manufactures of the 18th and 19th centuries, including Meissen, Vienna, Capodimonte, Wedgewood, and Doccia: I'd like to point out the Sèvres service that Napoleon gave to his sister Elisa, Duchess of Lucca.
The garden continues along the city walls, with a long wing to the right. This is where I suggest continuing your walk along the so-called Viottolone, a large avenue of cypresses with classical statues and carved sculptures from the Baroque era.
Walk for a while and you'll reach a large circular basin surrounded by hedges and statues: this is the 17th-century Piazzale dell'Isolotto. Surprise! Two walkways give you access to the island in the middle of the pond. Here at the center, adorned with vases and statues, you can see the beautiful Ocean Fountain, one of the first monumental works of Giambologna, a sculptor of French origin who flourished in Florence towards the end of the 16th century.
Your stroll along the Viottolone continues to the bright Lawn of Columns, and ends with an ornamental composition of ancient and Renaissance sculptures.
Walking along the medieval wall you'll return towards the city center, as always, accompanied by beautiful sculptures. After the Limonaia, the old greenhouse where the citrus pots were placed in winter, go up a slight hill until you are in front of the Meridiana, which is the last building attached to the back of Palazzo Pitti: it is a refined Neoclassical building that was built in the second half of the 19th century.
Now two fascinating collections await you: the Contini Bonacossi Collection, which can be visited only with reservations, and the Costume Gallery. You can follow the evolution of men's and women's fashion in thirteen rooms with about 6,000 garments there. You'll see the clothes found in the tombs of Cosimo I and his wife, recovered after an extremely delicate restoration.
FUN FACT: you may have noticed two strange, dome-shaped, partially-underground buildings in the gardens: two ice-boxes. Every day ice was brought in for the Grand Duke's food from Abetone, a city in the mountains 80 kilometers from Florence. In short: two ancient refrigerators!