This one is tricky, so I’m going to start by quoting Michael Swan:
“The is used with a number of rather general expressions referring to our physical environment – the world around us and its climate. The suggests that everybody is familiar with what we are talking about.”
Do you get what he means? This is why we refer to “the mountains” and why we say “I’m going to spend a lot of time at the beach this summer” even if we aren’t talking about specific mountains or a specific beach.
Here are a few general guidelines:
Natural Landforms and Settings:
We use “the” with natural landforms and settings when referring to them in a general sense. For instance:
- “I love spending time in the mountains.”
- “We went for a walk along the beach.”
- “Birds are abundant in the forest.”
Again, I’m not talking about any specific mountains, any specific beach or any specific forest.
Geographical and Recreational Contexts
When these natural environments are discussed in terms of their geographical or recreational significance, “the” is used to denote the typical features associated with them:
- “The desert can be really dangerous for hikers.”
- “Tourists flock to the beach during summer.”
- “The countryside offers a peaceful retreat from city life.”
Same as above – I’m not talking about any specific desert, any specific beach or any specific countryside.