Three days covers Madrid at one big museum per day

Or two city days and Toledo, 33 minutes by high-speed train

Day 1: old Madrid, lunch in La Latina, sunset at the Templo de Debod

Day 2: the Prado for the morning, Retiro Park in the afternoon

Day 3: the Thyssen, then Guernica in its free evening window

On a Sunday, put old Madrid and La Latina after the Rastro

In July and August, keep the museums for the afternoon heat