Many times an "open door" from God is one that allows our faith to be stretched and strengthened. That, after all, is God's objective for us: to grow in faith and Christ-likeness.
Take your opportunity or "open door" to God and ask for his confirmation - through his Word and godly counsel from others - and his peace in the decision, and you can have the assurance that you aren't just choosing a door at random, but you're carefully walking through the ones he wants you to enter.