Spotted via TRF, this video explores an abandoned Aerojet facility in South Florida, where the huge AJ-260-2 solid rocket motor was assembled and tested. The casing still is still on-site in an underground bunker. According to astronautix.com, this motor was considered as a possible first stage for the Saturn IVB. Rather than being factory-built and delivered in segments, the AJ-260-2 was cast in situ. Check out the specs of the 1/2 length prototype :
Thrust (sl): 16,013.400 kN (3,599,956 lbf). Thrust (sl): 1,632,933 kgf. Propellant Formulation: PBAN.
Status: Study 1965.
Gross mass: 831,345 kg (1,832,801 lb).
Unfuelled mass: 85,321 kg (188,100 lb).
Height: 18.29 m (60.00 ft).
Diameter: 6.60 m (21.60 ft).
Thrust: 17,695.30 kN (3,978,062 lbf).
Specific impulse: 263 s.
Specific impulse sea level: 238 s.
Burn time: 114 s.