The National Museum and Murabba Palace in the morning, then Masmak Fort and the Imam Turki bin Abdullah Grand Mosque; rest before iftar.
Day 2
Diriyah
At-Turaif in the late afternoon light, then iftar or a late dinner on Bujairi Terrace overlooking the ruins.
Day 3
Modern Riyadh
The Kingdom Centre Sky Bridge and Al Faisaliah, then KAFD by metro to see its towers and Zaha Hadid’s station.
Day 4+
Go further
A licensed tour to the Tuwaiq escarpment, or a long drive to the mud-brick village of Ushaiqer.
Honest thought: Riyadh is big and car-shaped. Use the metro for the main axis and taxis for the rest. In Ramadan, keep mornings for museums, rest in the afternoon and plan evenings around iftar.