der Berg
mountain
A large, natural elevation of the earth's surface that is significantly higher than the surrounding land.
Wir sind auf den höchsten Berg der Region gewandert.
We hiked up the highest mountain in the region.

mountain
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mountain
A large, natural elevation of the earth's surface that is significantly higher than the surrounding land.
Wir sind auf den höchsten Berg der Region gewandert.
We hiked up the highest mountain in the region.

As with many location expressions, 'Berg' (mountain) distinguishes between direction (accusative) and location (dative). You travel 'in die Berge' (to the mountains, acc.), but you hike 'in den Bergen' (in the mountains, dat.).
Im Sommer fahren wir oft in die Berge.
In summer, we often go to the mountains.
To describe a large amount, the structure 'ein Berg' (a mountain/pile) + noun is used. The noun often comes directly after it, without a preposition.
Ich muss heute noch einen riesigen Berg Wäsche waschen.
I still have to wash a huge pile of laundry today.
The idiom 'über den Berg sein' (to be over the worst) is a fixed unit. It means that someone has survived the most difficult phase of an illness or crisis. The person who has made it through is the subject of the sentence.
Nach der Operation war er schnell wieder über den Berg.
After the operation, he was quickly over the worst again.
The expression 'mit etwas hinter dem Berg halten' (to hold something back) means to withhold one's opinion or information. It is often used in the negative to express that someone is very direct.
Sag mir die Wahrheit und halte nicht mit deiner Meinung hinter dem Berg!
Tell me the truth and don't hold back your opinion!
amount / crowd
'die Menge' and 'der Berg' can both express that there is a lot of something. 'Menge' is neutral and can refer to small, large, exact, or approximate numbers and quantities. 'Berg' is used figuratively when there is a very large amount of something and it seems like a big pile, for example work, laundry, or paper. So 'Menge' is generally suitable. 'Berg' sounds stronger and often somewhat burdensome, because it shows: this is really a lot.

Nach dem Urlaub wartet ein Berg Wäsche auf Lisa.
After the vacation, a mountain of laundry is waiting for Lisa.
Daniel kauft für das Fest eine große Menge Getränke.
Daniel buys a large amount of drinks for the celebration.