The best sights in any city, in my opinion, are those that steer well clear of the tourists. Off-the-beaten-track gems, cultural spaces and undiscovered landmarks that you get to enjoy all by yourself are just as worthy of seeing than any Eiffel Tower or Buckingham Palace.
A Barcelona cactus garden probably doesn't seem like much of an exciting, must-see thrill, but it is a fun botanical highlight that will teach you plenty about Spanish flora and treat you to a beautiful view over Barceloneta Beach and the harbour.
But first, breakfast baby.