Threshold is defined as any doorway or entrance; the starting point of an experience, event, or venture. Psychologically it means the strength at which a stimulus is just perceived. Other than that, it also means a level or point at which something would happen, would cease to happen, or would take effect, become true, etc.
This pictures depicted all of the definitions I stated. Landed at Chiang Mai International Airport, I was on my final steps to cross that door to an exotic land of Thailand, soon to embark on a backpacking trip from Chiang Mai to Phuket; with adrenaline rushed in my blood and heart beat excitedly.
– door to Chiang Mai, Thailand.