If you click on the Rainbow Bridge, you'll receive a pop-up telling you that you'll need to expand your farm to 34x34 to receive it. If you have a whopping 5 million coins available to spend, you can purchase the 34x34 Exciting Expanse expansion and do just that. However - wait for it - the feature seems to be bugged for some users. That is, I immediately purchased the expansion after seeing the bridge on my farm and yet it never showed up in my Gift Box. Users on the FarmVille forums have reported receiving it for fine, but that it also may show up as a just a black circle.
That being the case, let's file this one in the "Wait and See" category. If you're like me, and have already expanded but didn't receive the Bridge, it's time to break out those typing skills and contact Zynga Support to see what has happened. If you haven't expanded just yet, I'd suggest holding off, at least a couple of days, to see if the issue is fixed.
Have you expanded your farm just to receive the Rainbow Bridge? Did you successfully receive the item, or is your account also bugged? Share your experiences with us in the comments!