  We present a study of a large filamentary structure at z~0.73 in the field of
the COSMOS survey, the so-called COSMOS Wall. This structure encompasses a
comprehensive range of environments from a dense cluster and a number of galaxy
groups to filaments, less dense regions, and adjacent voids. It thus provides a
valuable laboratory for the accurate mapping of environmental effects on galaxy
evolution at a look-back time of ~6.5 Gyr, when the Universe was roughly half
its present age.
  We performed deep spectroscopic observations with VIMOS at VLT of a K-band
selected sample of galaxies in this complex structure, building a sample of
galaxies complete in galaxy stellar mass down to a lower limit of log(M/M_sun)~
9.8, which is significantly deeper than previously available data. Thanks to
its location within the COSMOS survey, each galaxy benefits from a wealth of
ancillary information.
  In this paper we detail the survey strategy and weighting scheme adopted to
account for the biases introduced by the photometric pre-selection of our
targets. We present our galaxy stellar mass and rest-frame magnitudes estimates
together with a group catalog obtained with our new data and their member
galaxies color/mass distribution.
  Owing to to our new sample we can perform a detailed, high definition mapping
of the complex COSMOS Wall structure. The sharp environmental information,
coupled with high quality spectroscopic information and rich ancillary data
available in the COSMOS field, enables a detailed study of galaxy properties as
a function of local environment in a redshift slice where environmental effects
are important, and in a stellar mass range where mass and environment driven
effects are both at work.
