How about a subscription to a magazine? Depending on your interests, there are lots ( Intelligent Life, The Economist, New Scientist).
I'm on the constituency exec committee of a political party and trustee of a local charity, which are both pretty stimulating. Schools are often looking for governors and prisons for independent visitors. Get involved in a community project ( our village is currently converting a disused shop into a creative community space).
Listen to radio 4, and the excellent free podcasts available ( I enjoy This American Life and The Guilty Feminist).
Find a 'culture buddy', who will join you for book readings, exhibitions etc. Learn from each other's interests and keep an open mind about what's out there.
My husband loves learning new things ( on his commute). He's found apps/ free courses in Mandarin, coding and now investment strategies ( God help us!)
We've just come back from WOMAD, where we had a great time and got our fair share of music, books, debate, culture.
There are loads of things you can do, and not all cost much or take up too much time. There's so much evidence around the importance of intellectual stimulation in maintaining our physical and mental health as we move through life. Enjoy!