Detection contours of SPT overlaid on Euclid (RGB) H, Y, and VIS imaging from the Q1 data release for four detections in our catalogs. Top row : two tSZ identified clusters from the SPT-3G EDF-S survey (Sect. 7). These images highlight the sensitivity of both SPT and Euclid to high-redshift galaxy clusters. Bottom row : two examples of DSFGs in the emissive SPT-3G source catalog (Sect. 6). In the bottom-left, we show a protocluster candidate characterized as a DSFG and associated with the approximately dozen red dots centered at the SPT location. In the bottom right, we show a strongly lensed DSFG candidate, identified by the “halo” feature at the SPT location indicated by an arrow. The visible arc may be an unobscured component of the background DSFG. This strong lens candidate is not identified in the Euclid Q1 strong lens catalog, possibly pointing to differences in strong lens selections between Euclid and SPT.