I’ll tell you. It’s called Ocean, it’s in Hackney, it has three auditoria, and it has been operating very successfully for months. But you’ll understand why it has scarcely appeared on the radar screens of the nation’s cultural traffic controllers, despite being heavily Lottery-funded, when I tell you who held a private party there last week: American pop diva Mariah Carey, in town to promote her new single.

You can’t imagine Ms. Carey choosing the Wigmore Hall, for all its late-Victorian, arts-and-crafts opulence. No: Ocean has the bars, it has the video screens, it has the industrial-strength interior fit-out to cope with crowds who are, shall we say, just a tad more boisterous than those you might find in a lunchtime concert at St. John’s, Smith Square.

And there’s another reason why it’s possible that you might not previously have been aware of Ocean. It is a big building, but it is all but invisible. This is because it has been carved out of two existing adjacent buildings, directly opposite Hackney’s Town Hall and the famous Hackney Empire theatre. Ocean is made from both the 1907 Carnegie-funded public library, and its neighbour, the former 1926 Central Methodist Hall.

It would be nice to say that Ocean had preserved and revealed the best aspects of those characterful old buildings, had set up a fruitful dialectic between modern pop culture and old traditions, rather as radical drama seems to work best in plush, bourgeois Victorian theatres - but no. Its buildings were by no means the greatest of their type, for sure, but what personality they did have, has been comprehensively obliterated inside. When you are in the 2,100-capacity main auditorium, you are actually in the original Methodist hall, complete with horseshoe-shaped gallery. This has been hacked about and made to look like any other pop venue, though the intimate proportions of the space remain. And yes, if you look upwards you can just make out some original column heads and cornicing: that’s about it.

Instead, Ocean has a number of contemporary art installations by Michael Brennand-Wood, such as his “Liquescent Door”. You mount the curved steps to the library’s original canopied corner entrance, and you find you can’t get in. However, there is a circular bubbling porthole in front of you. I suspect that some concert-goers may well relieve themselves, post-show, in this suggestive little niche. Rather better are Jacqueline Poncelet’s rich textile wall-hangings in the smallest auditorium, which also act as acoustic absorption devices.

Of course, people don’t go to such places for the architecture, despite architecture’s famously symbiotic relationship with music. There, you might say, is the difference between pop and classical cultures. But this would be unfair to Ocean’s programmers. Mainstream pop like Mariah Carey is not what they are about. They offer a very varied programme of all kinds of music including contemporary classical and jazz, with a strong emphasis on emerging bands and a huge variety of ethnic music, reflecting the cosmopolitan nature of the area. It is a pretty sophisticated mix, and it’s a shame the building does not provide an equally sophisticated response.