HercuLeS is an extensible high-level synthesis (HLS) environment. It removes significant human effort by automatically mapping algorithms to hardware, providing a valuable design assist to software-oriented developers. To enable accessibility and easiness of hardware design space exploration (DSE), HercuLeS overcomes limitations of known work: non-standard source languages, insufficient representations, maintenance difficulties, necessity of code templates, lack of usage paradigms and vendor-dependence. Specific aspects that are highlighted in this manuscript are: a) the in-nerworkings of the HercuLeS hardware compilation engine, b) manipulation of SSA (Static Single Assignment) form, c) automatic third-party IP integration, d) backend C code generation for compiled simulation, and e) an exemplary case of DSE. HercuLeS enables efficient hardware generation that can closely match the quality of results of a manually-developed implementation with much reduced human effort and time requirements.