The one that opens up the moment you have a child. Never again your life belongs to you, just like you owned your folk's for a few years and even now occasionally when you declare broke or incapable of dealing with your marriage (random examples only...) :P
Some days that space will fill up to the brim with goodness (kid learns to spell his/her name) and some others the space will be cold, dark and even scary. Today is one of those days, I can't wait for my daughter to walk. She loves gardens and plants, specially her bugambilia - this beauty on the left (it bloomed this year thanks only to my little personal gardener). And would happily crawl her way around our tiny yard to visit every little green patch that has survived to my nasty hands. So I can't wait for her to walk. We do physical therapy everyday with her since she was 1 year old and started noticing she was not crawling yet. We've seen so many doctors with so many different prognosis; she shows improvement but it takes time, a long time to notice the small changes taking place.
The husband's attitude toward the whole thing makes me turn green with envy, he deals with it. That's it. No drama, doubts, nor fear, jeez... Me? this dark pit in the middle of my chest threatens to eat me up.
We have had all kinds of help, our parents, therapists (they rock), the school nanny, our friends and families. I love them all for loving us so much and being always around when we need it. Suddenly the empty space feels a little less empty.