Close to Frome is Longleat, they may have the odd Rhino or two. On the old S'n'D is the Gartel light railway just South of Templecombe, I'm not sure about opening times. Yeovil also has a steam centre. Of a non railway nature, but be careful of trains and armour, there is the tank museum at Bovington, which has reminded me, that near Yeovil is Yeovilton home of the Fleet Air Arm Museum. Sometimes known as WAFU's, hopefully the mods won't pick up on this Jack speak.
SS