I loved the Famous Five stories, whether directly set on Kirrin Island or elsewhere, though I am aware that the invention of the mobile phone would put paid to most, if not all, of these stories if they were written now.
I enjoy both the Poirot and Miss Marple series but I'm nominating here one of Agatha Christie's Tommy and Tuppence novels in The Secret Adversary. The British world after World War One and with the prevailing fear of a Communist revolution in the UK are very well reproduced here and the story itself is a cracking adventure.
Who better to conjure up Regency romances? Pride and Prejudice, followed by Persuasion, are my favourite books here. I can visualise Pemberley thanks to Jane Austen's pen portrayals. I also know The Cobb at Lyme Regis well and whenever I re-read Persuasion the sights and sounds of that area I readily recall. Jane Austen is not heavy on description but gives enough to the reader to create the necessary images. A wonderful example of great writing.