In our practice of shikantaza or "just sitting" there is no object of concentration per se. Sometimes I will come back to breath-counting but only as a means of "cracking the whip" when my mind has wandered across the hill for too long, or when struggling with physical pain, then I return to just sitting. In a busy environment, I just try to let the noises, images, smells, other beings flow over me and through me. Every moment is perfectly still - is there anything that now does not contain? Does this moment arise and pass away? When you are in a quiet place, does the moment not contain all the noisy loud places as well? Dogen built a Buddha-hall in a single speck of dust, and within the hall, the entire world. And yet, we are also constrained by our senses and our intellect.
Everything is a potential object of meditation. "Earth, grasses and trees, fences and walls, tiles and pebbles, all things in the dharma realm in ten directions, carry out buddha work." Vending machines, turnstiles, escalators and clocks, stop lights and newspaper boxes. If letting them all in at once is too much, start with what's in front of you, or out the window, or the wheels underneath, whatever is resonating with you, and as they become familiar let the likes and dislikes of the rest of our crazy lives drop away.