I sometimes employ a visual meditation I based on an extinct school of Buddhism called the Pugdalavadans. In this practice, I sometimes envision myself as unconstructed, unknown, and utterly free of the things of the world of forms. I have entered a very deep trance using this method once.
The Pugdalavadans just to mention, believed in an alternative notion to the Atman called the Pugdala. The Pugdala is only perceived to exist through the Skandhas, but it is non-dualistic and minimalist compared to Atman concepts- because the Skandhas aren't trusted to tell you anything about it. It's like glimpsing that you have an essential, deeper self through a dark curtain.
If you can visualize yourself sitting and picture the things of the world of forms- sound, sight, impressions, and such as ebbing away from you like a wave- this is a visualization I use.
Another I've tried is hearing the sound of silence. Listening to the quiet. That caused a powerful mental reaction at the time I was doing it.