There are 2 racecourses in Bangkok:

Royal Bangkok Sports Club – Henri Dunant Road (Opposite Chulalongkorn University). You can see the course from the Rajdamri Skytrain but there is no public entrance on that road.
Royal Turf Club – Nanglerng

They hold races at each venue on alternate Sundays – or Saturday if the Sunday is Wan Phra – first race starts around 12.00 .

Best if you can go as a guest of a Member since the public Stands are not particularly pleasant for Farang – lots of Military Police around to keep the peace. For that reason there is no alcohol on sale inside.

Betting is all on the Tote system although there are numerous illegal bookmakers.

The horses are really Ponies by international standards.

Patrick