If you just one day tour in Barcelona you should definitely visit its Gothic-Quarter, the place having a unique atmosphere. Early morning is the best time to visit this place, to see its old gothic buildings and monuments, to absorb its unique atmosphere, to tune into the beat of old Barcelona's heart, and to feel amazing spirit of the city. The Gothic-Quarter is situated on the territory limited by la Rambla and via Laientana, the Mediterranean sea and ronda de Sant Pere. Here we can find buildings from ancient times built by the Romans.
Walking around the Gothic-Quarter with its cathedral, old monuments and ancient buildings, cafes, bars, and restaurants you suddenly feel disconnected from your usual routine and open to new experiences.
A day tour in Barcelona, especially walking tour around the Gothic-Quarter, is the best way to spend your day in Catalan capital learning its legends and history.
At the end of this improvised tour around the Gothic-Quarter you should visit the Els Quatre Gats bar. It has been serving tapas and drinks since the end of 19th century. Famous people like Pablo Picasso and Gaudý often visited the bar and maybe got their inspiration there. Try to visit it too and who knows maybe you will also find something important there.