沉睡 (chén shuì): to be fast asleep; (fig.) to lie dormant; to lie undiscovered

The baby was fast asleep in its mother's arms, still with a sweet smile on its face.

After a night of fighting the fire, the firefighters were so exhausted that they lay down on the grass and fell fast asleep.

The small town lay fast asleep in the embrace of the mountains, until the first ray of morning sunlight woke it.

In winter, many animals sleep deeply in their dens and do not come out until it becomes warm in spring.