Madrid's public transportation system is extensive and efficient. A day pass costs approximately 8€ and can be used on buses, the metro, and light rail. Keep in mind that taxi rides and car rentals can be expensive, so it's recommended to use public transportation whenever possible.
If you have more time, consider seeing more of Madrid's museums, such as the Reina Sofia Museum or the Thyssen-Bornemisza Museum. If you have less time, consider skipping a visit to one of the museums or the Royal Palace. Don't forget to try other classic Spanish dishes, such as paella or tortilla de patatas!