。
The curtain fell amid thunderous applause.
Literal
Ten-thousand-thunder's applause's within [at-の内に] curtain [subject-が] fell.
A highly literary sentence. 万雷の拍手 ('ten-thousand-thunder applause') is a set phrase meaning thunderous, uproarious applause — 万 ('ten thousand') used as a generic intensifier, and 雷 ('thunder') borrowing the sonic image. のうちに ('within,' 'during') is a formal temporal frame. 幕が下りる ('the curtain falls') is the standard end-of-play/performance idiom.