This page of the guide to Horizon Forbidden West contains all the relevant information about exploration.
Horizon Forbidden West is an open world game full of diverse locations, including the ruins of Las Vegas. As you explore, you will encounter many settlements that have unique architecture and style.
While exploring the vast world of Horizon Forbidden West, you can grab onto cracks in walls or other elements (protrusions, moving fan parts) that will allow you to climb even the highest peaks or structures. To make climbing a little easier, you might want to use focus and highlight the climbing path.
The grappling hook (called pullcaster in the game) allows you to quickly pull yourself to an object. You will be able to cover more distance in a relatively short time. However, this is not an option that can be used continuously as this tool can only be used at designated points.
In Horizon Forbidden West, Aloy has a new gadget - a shieldwing that allows her to glide across long distances. This will enable you to reach places that at first glance may seem unreachable. You can land at any point during your glide - just turn off the gadget and Aloy will land on the ground.
In Horizon Forbidden West, you will also have to swim and dive to reach certain areas. Remember that by pressing the right analog stick (R3), you will move much faster. Importantly, Aloy's oxygen is limited, so staying underwater for too long can kill her.
In Horizon Forbidden West you can find a diving mask that will eliminate this problem. You can read more at: Diving mask - how to get it?.
Some elements of the environment, such as ventilation shaft hatches or cracked walls, can be opened or destroyed with the pullcaster. You will get the tool during the first hour of gameplay and after that you will be able to use it freely.
The pullcaster can also be used to pull loot crates that are out of Aloy's reach.
In some places you may find characteristic cracked panes of milky glass, which can be destroyed. You can find some loot in such hidden rooms, and sometimes reaching a hidden area will be linked to a mission in Horizon Forbidden West.
As you explore the map in Horizon Forbidden West, you will also come across walls covered in red flower-shaped crystals. You will be able to destroy this obstacle later in the game, when you make enough progress in the story.