I am away regularly for long periods of time on these exact type of conditions, except that I don’t even get an evening meal most of the time (although I do get a higher meal allowance usually).
Mine are never structured, but if I were away Sunday-Thursday nights, I’d create a bit of a routine.
Sunday - long trip there so just chill in room with TV.
Monday - long walk / gym / swim if facilities nearby.
Tuesday - research public transport from business park to city centre and get yourself into town for a walk or to eat somewhere cheap - street food?
Wednesday - “social” outing - get yourself on the internet and find a cheap show, last-minute discounted tickets to an exhibition or museum, free attractions (London for example will have so many options) £10 cinema ticket? I get saving but you also need to live a bit even when going away - maybe not every week but do it a couple of times.
Thursday - TV night in again in preparation for the trip back home.
If your social batteries get drained mid-week, swap and do the most demanding activity on Monday, and keep the walk or exercise for Wednesday.
Are you there on your own or with colleagues? My work trips are often in a group of 60-70 people, internationally, so lots of hours spent with them on trains, planes, and then at the work setting itself. So when the evening comes I usually really look forward to having a bit of time on my own - but when I do travel in a smaller group or on my own, I try to connect with local colleagues for one or two days a week in the city/cities I’m at.