You need to look on gov.uk for the official advice. Any other website, unless it directly quotes gov.uk, is likely to be personal opinion, and not everyone gets it right. The police guidance is also useful.
Asking on here totally pointless, people will quote time, distance and frequency limits, none of which exist, not in England anyway.
If you want to visit a hospital, you need to ask them, no-one else knows what an unnamed hospital will allow you to do.
The cycling that you refer to may be outside the guidelines, but if you're not a cyclist, your judgement about what is 'off grid', 'many miles' or 'at risk of accident' may not be reasonable either.
The responsible mountain biking community has suggested 'not far, not gnar (short for gnarly, ie fast downhill, jumps, steep rough terrain), no car' as a 'rule' but driving for exercise is not banned, although congregating in popular locations is generally unreasonable, due to lack of social distancing.