Does anyone do one?

I do ...

Whats it like?

What do you mean? It is humanities rather than science, so I don't know if that makes a difference ...

No I mean a PhD between two departments.

my project is by topic, content and methods interdisciplinary. formally i am getting a degree in a single discipline, however. it is organized in that within the department there is a specialist research centre.

i have a suspicion that doing interdisciplinary research at PhD level makes getting funding difficult. but that might just be me.

what kind of interdisciplinarity are you looking at? why are you asking?

I have the funding I'm just interested in peoples experiences of working in two departments or faculties. I see it as double the fun.

Okay. I work in an entirely interdisciplinary centre, rather than two departments, so I don't have much of a problem with that. However, my PhD itself will be from one discipline (rather than interdisciplinary), which is a bit irritating in terms of trying to get a job ...

I do, I get funding from both research groups to make up the total amount. I attend meetings for both groups but have a primary group and department which is where I spend all my time.

Both my supervisors are excellent and I love having input from different aspects.

I also get to go on two lots of group outings like xmas do etc.

I know someone who did Physics/Molecular Biology. I would expect it to be a struggle as he didn't have any background in Molecular Biology and had to learn the labwork from scratch. It depends how much emphasis there is on each department, e.g. is it just a year or a short project in one department. Could mean more work as widens what you need to know. Also whether the supervisors are going to really care about your progress and make sure you learn everything and not just leave you to it. I know someone else with supervisors at different unis, who did his 1st year in our lab, then finished at the other lab (similar departments). He did fantastically well in his 1st year (jammy), but his other supervisor was really unpleasant. He's finished and has a job in a brewery now(jammy).
There is the view that subjects have more cross-over now, and the different approaches give a new angle that no-one would have found otherwise.