2 sentences

1. 考古学在过去被认为是一个很冷门的专业。

   kǎo​gǔ​xué zài guò​qù bèi rèn​wéi shì yī gè hěn lěng​mén de zhuān​yè.

   Archaeology was considered an obscure major in the past.

   Source: Dong Chinese Dictionary

2. 昨天的比赛爆出了一个大冷门，夺冠热门竟然输了。

   zuó​tiān de bǐ​sài bào​chū le yī gě dà lěng​mén, duó​guàn​rè​mén jìng​rán shū le.

   Yesterday's match saw a major upset; the favorite to win actually lost.

   Source: Dong Chinese Dictionary