Under 3 hours after immigration, stay airside at both airports. Suvarnabhumi is vast and crowded, so eat and settle near your gate early. Don Mueang is smaller but its terminals are more hectic to move between, so the same rule applies: get food and stay close to your boarding gate rather than exploring.
If you clear immigration at Suvarnabhumi with 3.5 to 4 hours free, Lat Krabang is the one realistic option outside the terminal. It's the district the airport sits in, about 10 to 20 minutes by taxi (roughly 150 to 250 THB), with a local day market and Wat Lan Boon temple. It will not feel like a trip into Bangkok, but it gets you outside the terminal for an hour or so. Save the Erawan Museum and the floating markets for a 6-hour-plus layover; they need a longer round trip to be safe (see the 3-6 hour plan below).
A 6-hour layover from Suvarnabhumi leaves about 3.5 hours after you clear immigration and get back for boarding. That's enough for one focused destination, not a city tour.
From Suvarnabhumi (BKK): Take the Airport Rail Link to Phaya Thai (26 min, 45 THB), then BTS to Saphan Taksin, then river taxi to Tha Tien (40 min total, ~100 THB). Spend 60-75 minutes at Wat Pho (entrance 200 THB), then return the same way, leaving the temple by the 3-hour mark of your layover.
From Don Mueang (DMK): A1 bus to Mo Chit BTS (30-45 min, 30 THB). Chatuchak Weekend Market is a 5-minute walk from Mo Chit (Sat-Sun only). Browse for 90 minutes, grab street food, and return. For weekdays: take BTS to Siam for MBK Center or Siam Paragon (15 min, 44 THB round-trip).
On weekends, Bang Nam Phueng Floating Market is a lower-key alternative to Wat Pho: 25 to 45 minutes by taxi depending on traffic, open Saturday and Sunday only, with canal-side food stalls and short boat rides. It only fits on the longer end of a 6-hour layover, 5 to 6 hours after immigration, since the return trip alone can take an hour in weekend traffic.
Skip the Grand Palace on a 6-hour layover. The security queues and dress code checks add 30+ minutes, and it's 50 minutes by transit from Suvarnabhumi. You'll be rushed.
Bangkok's traffic is unpredictable. Avoid taxis during 7:00-9:00 AM and 4:30-7:30 PM. The ARL and BTS run on time.
With 8 hours between flights, you have 5-6 hours in the city. That's enough to visit two areas or add a riverside meal to a temple visit.
Classic 8-hour route from Suvarnabhumi: ARL to Phaya Thai, BTS to Saphan Taksin (40 min, 90 THB), then river taxi to Tha Tien for Wat Pho (10 min, 15 THB). Temple visit: 75-90 minutes (200 THB entrance). Lunch at a Tha Tien riverside restaurant (60-90 min, 200-400 THB). Return via river taxi + BTS + ARL (60 min). Leave the restaurant by hour 5 of your layover.
Weekend alternative from Don Mueang: A1 bus to Mo Chit, walk to Chatuchak Market (40 min). Market browse + food: 2 hours. BTS to Siam (15 min, 44 THB). MBK Center or Jim Thompson House (1.5 hours). Return via BTS + A1 bus (60 min).
For 10+ hours, add the Grand Palace (90 min on-site, 300 THB entrance) or take a dinner river cruise from Asiatique (2 hours, 600-1,200 THB).
Luggage storage is available at both airports: Suvarnabhumi charges 100 THB for 24 hours (basement level, Baggage Claim Hall), Don Mueang charges 100 THB for 12 hours (3rd floor, domestic terminal).
Pick a central base and move slowly. Riverside or old town areas are great for food, temples, and short walks. Heat, traffic, and crowds can be intense, so plan indoor breaks and avoid peak rush hours when returning.
