ACT0102 MUSE field of view overlaid on a HST colour image (where the filter F435W is blue; F606W+F625W+F775W+F850LP is green; and F105W+F125W+F140W+F160W is red). Green lines show the MUSE mosaic footprint, which is composed of three pointings with an exposure time of ≈2.3 h. Cyan (dashed) circles indicate spectroscopically (photometrically) selected cluster members (see Fig. 6). Galaxies marked with magenta boxes belong to the group at z = 0.63 (see Fig. 5). The multiple images used in our strong lensing model are shown by white crosses, and all the multiple image families have secure spectroscopic redshift measurements.