Feel like a level designer: 7 level editors
A level designer is a person who creates levels. He uses the available resources like a constructor: he takes scripts, sounds, models, animations, and other game elements and assembles them into a map based on the technical requirements. A level designer must create interesting gameplay, work with game engines, have good taste, and find a compromise between artistic and technical requirements for the project.
Before you sign up for a course on level design, try to create your own level for your favorite game. This way you'll get a portfolio and understand how much you like the profession. Don't use other modifications: work only with the content that was already created by the developers. Filling your locations with custom sets of weapons, armor, and game objects are considered bad taste among developers, especially when it comes to portfolios. After all, the whole art department works on creating the visual concept, and custom modifications often break the overall style and affect the game performance.
As soon as you realize that making levels is your life's work, master prototyping on Unity or another popular engine. In the meantime, here's a list of games with built-in map editors for those interested in trying their hand at level design.