。
She turned off the lamp to enjoy the moonlight.
Literal
She [topic-は] moon [possessive-の] light [object-を] enjoy [in-order-to-ために] electric-lamp [object-を] extinguished.
A small, contemplative sentence with deep cultural pull. Moon-watching has a long pedigree in Japanese aesthetic life — from the Heian-era courtly habit of 観月 ('moon viewing,' often accompanied by poetry-writing parties) to the autumn tradition of 月見 (gazing at the harvest moon with offerings of dumplings and pampas grass). The grammar is straightforward purposive ~ために ('in order to'): the dictionary form 楽しむ links to ために, and 電灯を消した supplies the action taken toward that goal. 月の光 ('moon's light') uses の possessively, the standard noun-noun glue.