Level 1: System Context diagram | Level 2: Container diagram | Level 3: Component diagram | Level 4: Code diagram
System Landscape diagram | Dynamic diagram | Deployment diagram

Code diagram

Code level diagrams are not natively supported by Structurizr, because we would need to support the ability to model the complete variety of different technologies that you would naturally find at level 4 of the C4 model; including object-oriented programming languages, functional programming languages, procedural programming languages, relational data models, etc. This is not feasible or desirable because:

1. It's a lot of work.
2. Few teams use level 4 of the C4 model.
3. Many IDEs can generate UML class diagrams from existing code.
4. Many database tools can generate entity relationship diagrams from existing database schemas.

Structurizr does support a feature called image views though, which provides a way to include arbitrary PNG/SVG images in your workspace, and these can function as zoom-ins for level 4.