I asked a few times to be allowed to lurk around the offices, either directly one the day of the interview, or for a day prior to my starting date (but after having signed a contract, though). Helps to get a feel of the place at least, if not necessarily of your day job (but obviously, looking at your future team's activity is recommended here).

Generally it was positively received, although in large companies there was some deflection with "non-issues", like:

- "oh but you know, our insurance does not cover for you being here" (oh yeah? So I was totally covered during the interview?) - "we'd need to notify security" (hmm, I'm already here) - "you know, everybody is probably too busy" (I'd hope so...) - "not sure where we'll put you" (and when I start in 2 weeks, if that desk hasn't appeared, I also don't show up?)

And even with these casual "non-issues", I actually never was denied this. Usually I stuck for one or 2 hours.

1 company let me stay for a day (they had flown me in for the interview and wanted me to stick around, which says a lot already).

Another one allowed me to attend an entire day of team meeting. After I had received a contract, but still, something like 2 months prior to my starting date. And that actually is what made me accept the offer as I hadn't signed it yet.