A mountainous place has a lot of mountains.
hilly
flat
the mountainous region of New Mexico.
新墨西哥州的多山地区。
the more mountainous terrain of New Hampshire.
新罕布什尔州更加多山的地形。
You use mountainous to emphasize that something is great in size, quantity, or degree.
huge
The plan is designed to reduce some of the company's mountainous debt.
制定这个计划是为了减少该公司的一部分巨额债务。