I treated myself to some spherical ice moulds. Despite them having the appearance of something extravagant, they were actually quite cheap.
I bought them online from Tovolo/Amazon for about £9 and they were delivered within a couple of days. On arrival I eagerly filled them with water and put them in the freezer.
The finished effect is quite dramatic. The ice also takes a long time to melt, so it cools your drink without diluting it.
Although note that you will need a glass at least 7cm wide. A heavy whisky tumbler would be ideal.
The only glass I had to hand that was big enough was a martini glass. Nonetheless, it was quite fun to use.
Hmm. Who does this remind me of?
Oh yes. David Bowie with his crystal balls (and overly tight trousers) in the 1980s film Labyrinth.