There is a list of sights to visit within the Grand Palace complex.
https://preparetravelplans.com/grand-palace-bangkok-guide/
Near the Palace, I visit:
1. Sanam Luang - historical field like our Padang, nice to visit late afternoon when Thais visit for recreation.
2. Khao San Road- backpacker and night market district north of Sanam Luang.
3. National Museum- also north of Sanam Luang
4. Wat Po- famous temple known for massages and reclining Buddha. Adjacent to the palace.
5. Wat Arun- Temple of Dawn. prominent landmark. Take cross river taxi from Tha Tien (Pier 8) near to Wat Po
6. Wang Lang Market- I visit their fresh produce markets, including this one across the river. Pier N10 by Chao Phraya River Express from Pier N8 or N9 (Tha Chang)
7. Walk to Chinatown (2km or so)