good bike for roughly £400

I know this is asking a bit much but you got to start somewhere!
I live in Poland and have an old bike we bought about ten years ago and which I have used increasingly over the past couple of years and which I use throughout the winter, including going to my weekly parkrun running meetups throughout the winter and this is Poland where it can get pretty cold and snowy.

All this to say I need a fairly sturdy bike. My husband has talked me into accompanying him on rides through the local woods, which are quite hilly ( we live in the Tricity). I am in my mid 50's and pretty fit but not a fanatic at sports.

Could someone recommend a good all round bike, to be used on bicycle paths on tarmac as well as in rough cross country terrain and which will be used throughout the year? Any pointers welcome :) Thanks!

Check out Trek mountainbikes. I have three of them, all bought for about that price, or less. They have all been good!