On Sant Jordi Day (April 23), you'll find a few institutions in the city celebrating with their doors open. One is the Ajuntament de Barcelona (City Hall). You can visit the Escala d'Honor, the Galeria Gòtica and the building's centrepiece (and oldest part), the famous Saló de Cent, accompanied by figures from local history. Coinciding with the Open Day, the Ajuntament will once again sell roses to benefit local charities in their patio area from 10am to 8pm. The proceeds go entirely to not-for-profit organisations.
From 11am to 8pm, the Palau Savassona, home to the Ateneu Barcelonés, also opens its doors. Visit the library, garden, discussion rooms... and participate in the activities they'll have lined up. In addition, if you become a member of the Ateneu the week of Sant Jordi, they'll waive the sign-up fee.
If you're around Montjuïc, the Museu d'Arqueologia de Catalunya is also taking part in the Open Day, and you can get in for free from 9.30am to 7pm.