Both are fine, but probably 'in' would be viewed as best. 'at' the meadow gives extra prominence to the location (compared to the experience ); for example, you would say, 'meet me at the tree and I'll walk you to the road' - here meeting is not to experience the tree at all, it's just a location to do something else. 'in' is within the meadow, and gives more of an experience of what's around you.
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