I wonder what sizes are typically deer parks and similar enclosed spaces where ungulates like red or fallow deer, blackbuck etc. live not physically separated from visitor paths. And what are the smallest / narrowest successful examples?
I like a deer park, there are many happy hours to be had with a camera in one! There's some useful information on the history of deer parks in the UK here
What is a deer park? | Landscapes history
While deer parks date from the Norman conquest, many of the 'modern' ones were formed around the time of English Civil War and became attached to the grand houses and estates or grew up as part of the Royal estates (The version of Richmond park we have now was created as an enclosed deer hunting space by King Charles I for example). The feature these parks have in common is their size - none are small and will usually have fallow, roe and Red deer as well as Muntjac and Chinese (though neither of those are originally native of course) and some have Sika and other exotics.
The notion of deer parks is synonymous with the large estate. And then there are herds managed for shooting as well as farming venison.
Safari parks also have free roaming animals but obviously most of those are seen from a car, though Woburn, for example, has exotic and native deer in it's deer park which is not part of the safari but of course Woburn is an estate first with a Safari park in it.
In the main deer parks are by their nature large, sitting in large estates (Houghton Hall with the white fallows, Burghley park, Badminton estate, Chatsworth, the list is huge).
For an idea of size you can take a look at
Burghley House | Deer Park
or
Deer in Richmond Park
This link then gives you an idea of UK locations for deer; not all allow visitors to free roam with the deer but a large number do.
Where to see Deer - The British Deer Society
I believe the only location with free roaming Blackbuck is Watatunga in the UK which does escorted tours. So the visitor is not mixing with them per se.
In terms of smaller free roaming enclosures, New Forest wildife park has a smaller free roaming space (red deer are not free to roam but the other deer are) but I wouldn't say it was small, just not estate deer park size.