I have to echo the thoughts about the island Subway platforms in Glasgow (and it ain't just Kelvinhall - lots of them are similar). They are toatie! Can be rather unnerving standing on them waiting for the train to come in, particularly when it's busy and/or you're doing a Sub Crawl! In rainy conditions (not that that's common in Glasgow
) the platforms can also be very wet and slippery.
Originally, all the platforms were like that, although after the 70s refurb, side platforms emerged at the busier stations (IIRC; St Enoch, Buchanan Street, Hillhead, Partick, Govan, Ibrox). Some like Partick and St Enoch have two side platforms, others like Buchanan St and Hillhead had just the one with the original middle platform being used for one of the circles (the recent addition of a glass barrier again makes the experience a lot better!).
Back on the mainline, I'll also nominate High Street (Glasgow) for a narrow platform. It's fine at the West end, but as you move towards the East (only an issue for 6 car trains) they become really quite narrow, probably so that they can fit in the cutting.