From a reader…
We currently have a gymnasium-like church, with a wooden table for an altar.
We have no high altar behind it. How would we face east and Cdl. Sarah suggests for Advent if we don’t?
First, I hope that for Father’s sake and for the sake of the congregation, you will indeed have the chance to benefit from ad orientem worship.
Remember that celebrating “towards the East” is symbolic. It doesn’t have to be the literal geographic East. So long as you are all facing the same direction, you are symbolically facing the East whence our forebears – from the very earliest days – thought Christ would return in glory. Thus, we turn to the Lord who is coming. Given that the liturgical season of Advent is about getting ready for the “coming of the Lord”, really for the Second Coming more than the First, the beginning of Advent is an appropriate time begin offering Mass ad orientem.
There’s no need for reredos. Just put six tall candles on either side of the crucifix (and tabernacle if possible) on the back of the altar. The priest can then simply step around to the front. Instead of facing the congregation like an adversary or an entertainer (Mass adversus populum?), he and the congregation will be united in their orientation in a highly effective, manifest way.