I have 5 in - one goes out for a play for a couple of hours every few days (but not every day), one is on holiday and goes out most days for anything between 10 mins and 3 hours (he comes in when he asks to!)
The other 3 don't go out at all.
They have ad lib haylage, they are fit hunters and get worked virtually every day - and sometimes they get to go hunting!
I ride 4 of them in the morning/early afternoon - once each has been ridden, they are put back to bed and doze for the rest of the afternoon. They get tea about 5, & checked again with another feed and haylage again about half ten.
I don't consciously do anything to keep them interested ....but then I'm about and doing stuff most of the day. If I'm away for the day, and they have a peaceful day in, I think they're probably quite relieved!!
Mine are in every other day and at night, although with this frost i darent turn them out so they are in for a few days, the field is terribly chewed up its like a death trap in the frost!!
They go on the walker for 15mins for a leg stretch and i give them a graze in hand, one gets worked and they both get a groom!
My sec a 2yo gets a snack a ball with a handfull of nuts in to keep her occupied!
Mine is in when the weathers bad which is averaging two or three days a week at present. She's used to living out through the summer and at least being turned out daily over winter so I'm trying hard to keep her happy which she definitely seems to be so far.
Typically I would ride first thing then give her a long thorough groom in the yard, then she'll go back into her stable with a big pile of hay until late evening.
When I get back to the yard in the evening then she'll have some sort of evening 'exercise' typically a short walk and grazing in hand or loose schooling and carrot stretches. I try to do something that gets her using her brain, like some NH style groundwork for 10-15 mins too. Then back to the stable for more hay!!
In the stable, I hide apples, carrots and other treats in her hay for her to find. I've always liked the look of those treat balls but never got round to buying one.