The "new" gaol was completed in 1847. It was built with the aim of reform by isolation. It contained a central pentagonal building of 84 cells, two lockup rooms, ten turnkey's rooms and ten yards.
Each cell had stone walls and floors and a timber ceiling; was 6ft long, 5ft wide, almost 11ft high, and was occupied by up to three prisoners.
The complex also contained another 40-cell block, two service buildings, and 12 solitary confinement "apartments" about which the Royal Engineer wrote "... the convicts regard the ... new cells with dread ... they are the most perfect specimens of prison construction I have seen ...", and two "dumb cells" which prevented the transmission of light and sound - sending their occupants insane.