Spend a relaxing afternoon at Retiro Park, the largest park in Madrid, where you can paddle a boat on the lake, visit the Crystal Palace, and enjoy the greenery.
You can walk to Retiro Park from Mercado de San Miguel.
End your day with a traditional Spanish dinner at Sobrino de Botín, the oldest restaurant in the world according to the Guinness World Records, known for its classic Spanish dishes.
From Retiro Park, take a taxi or the metro to get to Sobrino de Botín.