Bangkok is large and its heat, especially by mid-morning, limits how much continuous walking is genuinely comfortable, so the most enjoyable approach tends to be short, focused walks around specific areas like the old city around Wat Pho and the Grand Palace, rather than trying to cross the city on foot.
Pavements can be inconsistent, narrow in places and shared with parked motorbikes, food carts and uneven surfaces, so a slower, watchful pace suits the city better than a brisk stride. Pedestrian bridges and marked crossings are worth using given the intensity of traffic on major roads.
The Chao Phraya river and its network of canals offer a genuinely different way to see the city, with river boats providing both transport and a scenic break from walking in the heat, particularly useful for reaching temple sites along the water.