Abstract
This paper represents a journey with look-back time, using the interplay between clusters of hot young massive stars and the interstellar medium, by means of spectroscopy of violent star-forming regions from the nearby giant H II regions 30 Dor in the LMC and NGC 604 in M33, to star-forming galaxies at intermediate and high redshifts (z > 0.1 to z ≡3), reaching the Big Bang nucleosynthesis realm at z > 1000000. Included in the journey are also the promising prospects for the near future, for studying similar objects enshrouded in dust up to z ≡10 - 20.
