Trips to greenhouses and conservatories are a great idea for a good number of reasons. However, don’t read the rest of this if you don’t want any spoilers.
spoilerGreenhouses, in general, may not be a very reliable way to get a nice vitamin D boost. I’ll spare you the details, but most of the covering materials specifically developed for greenhouse use will significantly reduce or outright block UV light. You may still get some limited UV exposure, but you wouldn’t want to go into that situation with the expectation of getting a nice boost in vitamin D from it.