lots of fun techniques, a common one for getting down low enough where other methods become practical is stirling cryocoolers, and those are even on ebay for a few thousand (cascade refrigeration systems, and joule thompson coolers, and a few others are also used), way down past that theres stuff like weird magnetic coolers, and dilution coolers All very interesting, reading about exotic cooling methods is quite fun.
hermione was criticized a lot by pretty much everyone when she tried to free the house elves and made badges etc.