  We demonstrate a miniaturised and highly robust system for performing
Doppler-free spectroscopy on thermal atomic vapour for three frequencies as
required for cold atom-based quantum technologies. The application of additive
manufacturing techniques, together with efficient use of optical components,
produce a compact, stable optical system, with a volume of 0.089 L and a weight
of 120 g. The device occupies less than a tenth of the volume of, and is
considerably lower cost than, conventional spectroscopic systems, but also
offers excellent stability against environmental disturbances. We characterise
the response of the system to changes in environmental temperature between 10
and 30$^{\circ}$C and exposure to vibrations between 0 - 2000 Hz, finding that
the system can reliably perform spectroscopic measurements despite substantial
vibrational noise and temperature changes. Our results show that 3D-printed
optical systems are an excellent solution for portable quantum technologies.
