Thailand is split between the frenetic energy of Bangkok and everything else. The capital is unrelenting: street food, night markets, temples tucked between shopping malls, traffic, energy, constant stimulation. It’s not restful, but it’s never boring. Most people spend 3-4 days, then escape.
The islands dominate the tourism conversation. Phuket is the gateway, while Krabi is nearby and feels slightly less overrun. Koh Samui is party-oriented. Koh Phangan is where Koh Samui’s younger sibling lives. Koh Lanta is quiet, less developed, genuinely peaceful. The Andaman region has the best diving and best beaches. The Gulf side (Koh Chang, Koh Tao) is closer to Bangkok and slightly less crowded.
Northern Thailand (Chiang Mai, Chiang Rai) is cooler, mountainous, less crowded than the coast, with temples, night markets, and access to hill tribes and elephant sanctuaries. Central Thailand has Ayutthaya (ancient temples, historical sites). The south coast has caves, waterfalls, and the massive limestone formations. Most visitors do island time, then either head north or back to Bangkok. The infrastructure works everywhere. You can be as isolated or connected as you want. Weather shifts dramatically seasonally, so timing matters. English is widely spoken in tourist areas, less so elsewhere.