The hotel lobby was decorated sumptuously with crystal chandeliers hanging from the ceiling.

sumptuously 是形容词 sumptuous 的副词形式。sumptuous 来自拉丁语 sumptus（花费），形容"奢侈的、豪华的"。加上-ly 变成副词后表示"豪华地、奢侈地"，用来描述装饰的奢华程度。