I spent almost my entire childhood summer holidays in the Lake District in the north of England, reading Arthur Ransome's "Swallows and Amazons" books. We therefore spent a great deal of time tracking down the various locations features in the book.

• Wild Cat Island
  Wild Cat Island is on Coniston, it is very close to the eastern shore of the lake and is towards the south of the lake. The harbour is at the south of the island and is the best place to land (you could use the landing place but that is strictly for natives). All the features of the island are there except the lighthouse tree which, sadly, is no longer there.
  
  
• Rio
  Rio is Bowness on Windermere. Looking at the map in the book, almost every detail of Rio, Long Island and Rio Bay can be found in Bowness Bay, including the Hen and Chicken rocks, the steamer pier and the position of the islands. Bowness is on the east coast of Windermere and is an ideal place to visit. A climb to Orrest Head, about 20 minutes walk from Windermere Station is recommended for the best views of the lake.
  
  
• Long Island
  Long Island is Belle Isle, opposite Bowness on Windermere. This island is famous for its round house (which was recently damaged by fire) and the house's eccentric owners, one of whom had an amphibious car which he used to drive to the mainland every day.
  
  
• The Houseboat
  The actual houseboat is now used on Lake Coniston to give tours of the lake, including the Swallows and Amazons tour. It is worth a visit if you are short on time, but if not I recommend hiring a boat and doing the tour yourself (this way you can land at Wildcat Island).
  
  
• Cormorant Island
  Cormorant Island is also on Windermere, It is a couple of miles south of the ferry, close to the east shore.
  
  
• Kanchenjunga
  Kanchenjunga is Coniston Old Man. This is one of the easier of the big peaks in the Lake District and gives wonderful views of the surrounding lakes and tarns. There is a cairn at the top, but I could find no sign of the biscuit tin buried under it.
  
  
• Amazon River
  As far as I can gather, the Amazon River is at the south of Lake Windermere, where the lake narrows and becomes a river. If you want to see this, the best idea is to spend a few hours at Fellfoot Park where boats can be hired to take the trip up river. It is a great place to go swimming, as the entire width of the river is not more than five feet deep at this point. The Amazon may also be one of the feeders of the Pull Dyke, at the northwest and of Windermere (thanks Tiefling).
  
  
• Secret Water - contributed by Tiefling
  Secret Water is the Naze, in Essex. This is very close to the locations in "We Didn't Mean to go to Sea", all of which are real (see Pin Mill below).
  
  
• The High Topps - contributed by Tiefling
  The High Topps is Little Arrow Moor, to the south of Coniston Old Man. It is dotted with the old mine workings, as described in Pigeon Post. Warning to propective Copper miners, it is no longer legal to just open up an old working and start blasting.
  
  
• Pin Mill - Contributed by nevermind_me
  The Butt and Oyster pub in the village of Chelmondiston, on the River Orwell, Suffolk, is Pin mill of 'We didn't mean to go to sea' fame.
  
  

When I find it I will look in my "Discovering Arthur Ransome" book and add a lot more, but these are the most interesting and recognisable of the areas in the book.