I love books! When I think "relaxing space", I think of a quiet café or a "snug" (quiet nook) in a country pub, with bookshelves overflowing with books. These spaces are best when the patrons are encouraged to read them, but it feels cosy just seeing them there for decorative purposes.
My personal favourites are:
THUD! by Sir Terry Pratchett. The story begins with the murder of an important dwarf in Ankh-Morpork, leading to unrest on the lead-up to the anniversary of an ancient (but not forgotten) war between dwarves and trolls. Meanwhile, Commander Vimes is dealing with the initiation of the first vampire into the City Watch, which brings plenty of problems of its own. If you have never read any stories from the Discworld series, I recommend the Watch if you like mysteries and the Witches if you like mad quests with lots of hijinks.
The Hound of the Baskervilles by Sir Arthur Conan Doyle. It's creepy, unsettling; chilling. The Victorian language somehow adds to the atmosphere. Through most of the story, it is unclear whether there is a murderer at large or if it truly is the apparition of the monstrous hound at the heart of the mystery. This is the best known of the Sherlock Holmes stories and it is amongst the very best. On saying that, if you can easily obtain a treasury, I would recommend doing so; every tale is highly enjoyable.
Great Expectations by Charles Dickens. The story of Pip, who begins as a poor orphan, who was brought up by his volatile older sister and her kindly husband. He later comes into wealth and spends much of the story trying to find out where the money is coming from. A good story, with enjoyable (albeit often horrible) characters. I have many favourites by this author (and it was impossible to choose one). If you enjoy this story, I would also recommend Bleak House and Little Dorrit, though I have not found a story by Dickens that I have not enjoyed.
War of the Worlds by H. G. Wells. Told in first person narrative of an unnamed narrator from Surrey and his younger brother in London, this story documents the invasion of the Martians, beginning with the first craft to come to earth in Surrey. Jeff Wayne's musical version is not completely true to the book, but is also worthy of a listen.