Plaça del Rei is my favorite square in Barcelona, you have the feeling of walking in the medieval Barcelona through the Monumental buildings that are in the square. You can find the Royal palace, the Palau Reial Major as we call it and the buildings surrounding the palace are the perfect painting to see how it was the city in Middle Ages.
The Palau Reial Major is right at the back in Plaça del Rei and has a watchtower of King Martí on one side. The Palace was the residence of the counts of Catalonia from 13th to 15th century, the building has a gothic style and although the building can be traced back up to 11th century, the appearance is from the 13th century as there were so alterations made at the time.
One of the famous rooms inside the Palace is the Great Hall or Saló del Tinell, a spectacular room with its round arches that is the most representative space of the building.
Among the surrounding building we can find the royal Chapel of Santa Àgata, the Palau del Lloctinent or Lieutenant's Palace, the Casa Clariana-Padellàs that is now the city's history museum ( MUHBA), if you like history this is a must visit, you can go down to see what remains of the Roman Barcelona.
There are places of take away food nearby in Llibreteria street and in the are in general in Gothic, what locals and tourist do is to bring the food with them and seat in the stairs of the church in the same Plaça del Rei square. Perfect place to eat and to observe the square at the same time.
Disclaimer: Plaça del rei picture by Marc Mora