Two days is enough to see Bangkok's grandest temples, cruise its river, and still wander a market or two. This itinerary front-loads the Old City's must-see sights on day one, then balances a cultural museum stop with river life and modern Bangkok on day two.
Begin early at the Grand Palace, Bangkok's most visited landmark, then walk to nearby Wat Phra Singh before crossing the river for Wat Arun (Temple of Dawn), whose porcelain-covered spires are best photographed from the water. Take a Chao Phraya River Cruise back toward the center, stopping at Wat Traimit (Temple of the Golden Buddha) to see its solid gold Buddha image. Spend the evening in Chinatown (Yaowarat), where street stalls and neon signs make for an easy, food-focused wind-down after a heavy sightseeing day.
Devote the morning to the National Museum Bangkok for context on Thai history and art before the day gets busy. From there, climb Wat Saket (Golden Mount Temple) for panoramic views over the old city. In the afternoon, browse the stalls of Chatuchak Weekend Market if it falls on a weekend, or shop at Siam Paragon Shopping Mall as an any-day alternative. Close the trip with a relaxed walk through Lumpini Park or a stroll along Silom District as the city lights come on.