Next retreat: TBD. 

I do quarterly stillness retreats with my meditation group. The retreat is over 4 days. Each day we sit in uninterrupted stillness for 3 hours. The reason I do it over 4 days is to accommodate the European students. You can join any one session if you like if you can’t do all four, but ideally all 4 for deeper experience. 

Each 3-hour session is about immersion (samāveśa) in the heart center, allowing ourselves to abide in stillness in the heart, and surrender to be worked by higher intelligence. 

“When there is an absorption into the Heart maintained for four periods of three hours, it assumes the nature of a 'day' in which everything is permeated by the light of consciousness and the night of contraction ceases, one becomes omniscient like Bhairava in this very body." 

From the Parātriśikā Laghuvṛtti, attributed to Abhinavagupta, translated by Ben Williams