Thanks for your input, JGH!
As a matter of fact, open-air locations are on our wish-list since Day One: Classical Greek theatres, open air arenas for opera, medevial city squares, even forests have been looked for and discussed already.
The main reason we didn't capture any of them up to now is simple: It's more or less undoable. 8-/ ... Unlike all other convolution-based products on the market, MIR relies on thousands (!) of impulse responses from a selected Venue. During these day-(or rather night)-long recordings two problems would arise out there in the open: Many, many sources of noise are everywhere, and each of them can render any of these 60 seconds of IR recordings unusable (wind, birds, planes, passing cars or people ... you name them). OTOH, listening for 24 hours or more to sine sweeps in concert volume (85 dB in a free-field measurement!) is hard for _us_ --- but it's intolerable for any creature in the neighbourhood, be it a human or an animal.
Regarding your suggestion to record MIR Venues in a "castle": What do you have in mind?
Thanks again for sharing your ideas!