瞒天过海

In 643 AD, Emperor Taizong of Tang baulked(犹豫，阻止) from crossing the sea to a campaign against Koguryo. His general Xue Rengui thought of a stratagem(策略，计谋) to get the emperor across and allay his fear of seasickness.

On a clear day, the emperor was invited to meet a wise man. They entered through a dark tunnel into a hall where they feasted. After feasting several days, the Emperor heard the sound of waves and realized that he had been lured onto a ship! General Xue drew aside the curtains to reveal the ocean and confessed that they had already crossed the sea.

Upon discovering this, the emperor decided to carry on and later completed the successful campaign.