You can simply drop the mains down with a 'ballast resistor', using a constant load to keep the voltage the same - but it's very wasteful in generating loads of heat. Instead of a resistor you can use a 'capacitor ballast', which doesn't generate loads of heat, but does require a suitably rated capacitor - and usually of a perculiar value.
Both methods have been used over the years, the capacitor version is probably best - particularly with such a large drop.
In both cases, everything in the circuit is live to mains, so you need to construct accordingly.