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Massive stars lose a large fraction of their original mass over the course oftheir evolution. These stellar winds shape the surrounding medium according toparameters that are the result of the characteristics of the stars, varyingover time as the stars evolve, leading to both permanent and temporary featuresthat can be used to constrain the evolution of the progenitor star.  Because long Gamma-Ray Bursts (GRBs) are thought to originate from massivestars, the characteristics of the circumstellar medium (CSM) should beobservable in the signal of GRBs. This can occur directly, as thecharacteristics of the GRB-jet are changed by the medium it collides with, andindirectly because the GRB can only be observed through the extendedcircumstellar bubble that surrounds each massive star.  We use computer simulations to describe the circumstellar features that canbe found in the vicinity of massive stars and discuss if, and how, they mayappear in GRB observations. Specifically, we make hydrodynamical models of thecircumstellar environment of a rapidly rotating, chemically near-homogeneousstar, which is represents a GRB progenitor candidate model.  The simulations show that the star creates a large scale bubble of shockedwind material, which sweeps up the interstellar medium in an expanding shell.Within this bubble, temporary circumstellar shells, clumps and voids arecreated as a result of changes in the stellar wind. Most of these temporaryfeatures have disappeared by the time the star reaches the end of its life,leaving a highly turbulent circumstellar bubble behind. Placing the same starin a high density environment simplifies the evolution of the CSM as the moreconfined bubble prohibits the formation of some of the temporary structures.

On the circumstellar medium of massive stars and how it may appear in GRB observations