Four men have been jailed at Mold Crown Court for their part in a 'sophisticated' cannabis growing operation in disused railway runnels in Bangor, Gwynedd.
Gerald Davies, 63, from Bangor, and Kenneth John Vincent, 59, from Beaumaris was jailed for three years and four months.
They admitted producing cannabis and conspiring to supply the drug.
Philip Joseph Bigley, 22, from Liverpool and Christopher James McIntyre, 30, from Bootle, Merseyside both received sentences of 12 months after admitting production charges, having worked as gardeners at the site.
Mr Recorder Timothy Petts said the factory was capable of producing more than £1.5million worth of cannabis in a year.
Police had described the site as one of the most elaborate ever found in North Wales.