The practice of approaching outside void to awake inner void :
kūpādike mahāgarte sthitvopari nirīkṣaṇāt |
avikalpamateḥ samyak sadyas cittalayaḥ sphuṭam || 115 ||
"Standing over a well for instance
or a deep precipice, with eyes unblinking,
because attention is undivided,
the mind disappears truly, clearly and at once."