The noun 乐园 (lèyuán) means 'paradise,' 'amusement park,' or 'playground.' It is composed of 乐 (joy/happiness) and 园 (garden/park). It is commonly used in the names of theme parks and entertainment venues, and can also be used figuratively to mean an ideal, happy place.
孩子们在儿童乐园里玩得很开心。
Háizimen zài értóng lèyuán lǐ wán de hěn kāixīn.
The children are having a great time at the children's amusement park.
这座城市新开了一个海洋主题乐园。
Zhè zuò chéngshì xīn kāi le yī gè hǎiyáng zhǔtí lèyuán.
This city has newly opened an ocean-themed amusement park.
对他来说,图书馆就是他的乐园。
Duì tā lái shuō, túshūguǎn jiùshì tā de lèyuán.
To him, the library is his paradise.