On this page of the guide to Baldur's Gate 3, you will find information about exploration. You will learn more about how the camp works and how to find hidden passages.
The game features a huge map that you can explore freely, and your only limitations are terrain obstacles. Some of these can be bypassed by jumping, for example, but this is not always possible. In case of cliffs or tall buildings, you can also look for a ladder.
At some points you will also find passages to minor locations, such as undergrounds or dungeons. They are often hidden and can be located using perception checks. When the test is successful, the entrance will be highlighted and you will be able to use it. It also happens that there are several ways to get to a given place.
Check the map to see what part of the world you've already discovered (press "M" by default). This will show you what parts you've already seen, and which places you've discovered. Check the map by pressing 'M' if you're having problems reaching a given place in the world.
The world itself is vast, which is why a fast-travel system was implemented in the production. You discover more landmarks by exploring the map. You can fast-travel to any discovered landmark from the world map.
You can also move to the camp. The camp is a place where you have more time for conversations with other team members. You can also rest and regenerate your strength.
You can learn more about the camp in a separate section of this guide!