I've never worked inpatient psych (so forgive me if my ideas are totally inappropriate and useless), but I have worked for a long, long time in a homeless shelter, and many of our clients were indeed struggling with their mental health.
All of our most well-established programs are "drop-in," where the client can come and go as they like. 99% of the time there is coffee and treats, to entice people into participating. Some things that our clients really love are often things that seem really childish, but are fun and offer an opportunity for mindless stress relief, or allow space for good conversations. One example we used to call Lego Therapy. One of our staff had a bucket of Lego (a BIG one) and he'd just spread it out on a table and start building things. He was also very, very good at connecting with clients and enticing them into joining him. We used to do similar programming with board games and colouring books.
Other random programs our clients loved: Beauty Night (geared towards women, but involved things like manicures and haircuts and makeovers or whatever), movie nights, yoga classes, mindfulness groups, guest speakers about issues that affected our clients (lots of speakers on addiction, many on aboriginal issues, issues relevant to drug users, that kind of thing), and we had a number of really successful more therapeutically oriented groups, like grief and loss, addictions, women's group, that sort of thing (probably less relevant for you).