If you want some fun, try working with the allocation-minimizing parts of the standard libraries, or lambdas-as-Expression, or even Roslyn analyzers/generators.

If you want some fun, try working with the allocation-minimizing parts of the standard libraries, or lambdas-as-Expression, or even Roslyn analyzers/generators. C# has loads of "fun language features" to play around with, but what I find useful is that you can just use them boringly if you need to.