Trail running is awesome. I used to run 5k thru marathons. It was fun, but then tried running with a friend on a state park trail. We didn't push hard and just focused on enjoying the day and scenery and it was eye opening. It was still a workout because on rough trails you are always adjusting your stride, cadence and focusing on avoiding rocks, roots, etc. Definitely not mile after mile of the same thing.

I can do 50mi on a trail and feel much better at the end than a 1/2 marathon on concrete.

On the bike it's almost the same. I much more enjoy 100 mi on a nice scenic road than trying to get a KOM on Strava.