The second is "past" and the third is "time".
You've got me on the first one. Maybe a skyscraper?

If someone wants they can try this riddle - I just made it up.

You can fly to the limits of the sky and never encounter me.
Yet scale the highest mountains and I will be with you.
You can dive deep into the ocean and never encounter me.
Yet at the bottom of the canyons I will be there to greet you.
What am I?