探索/调查/理解类层次结构和新项目工作原理的最佳方法

Imagine such situation. You get some legacy code or get some new framework. You need to investigate and understand how to work with this code as soon as possible. There is no chance to ask for help from previous developer. What are the best practices/methods/ways/steps/tools (preferred .NET Framework tools stack) to use to get maximum efficiency in investigating new to you code base.Imagine such situation. You get some legacy cod