Where sea and sky meet
I love pictures where the edge between sea and sky is somewhat blurred and you can't tell where one ends and the other begins. You could just enjoy it when you see it happening but there is also a reminder here that the boundary between objects is not quite what it seems - where does one thing end and another begin?
You could go a bit deeper and ask yourself, where do my body and mind meet? (This is a direct method of introspection as opposed to the more labour intensive method of watching the breath). So, we sit there looking, looking, looking for the boundary between body and mind. We might get nowhere, or we might see something and we feel our head turning inside out and going all 'I'm going to pop' on us. There's a truth here but we can't think it. We want to hold it and know it but it eludes us and after a while we realise that it is perhaps time to return to the normal world and have a nice cup of tea.