The Siddhâsana

अथ सिद्धासनम्
योनि-स्थानकमङ्घ्रि-मूल-घटितं कृत्वा दृढं विन्यसेत्
मेण्ढ्रे पादमथैकमेव हृदये कृत्वा हनुं सुस्थिरम् ।
स्थाणुः संयमितेन्द्रियोऽचल-दृशा पश्येद्भ्रुवोरन्तरं
ह्येतन्मोक्ष-कपाट-भेद-जनकं सिद्धासनं प्रोच्यते ॥ ३७॥

Atha siddhāsanam
Yonisthānakamangghrimūlaghatitam Krtvā drdham vinyaset
Mendhre pādamathaikameva hrdaye Krtvā hanum susthiram
Sthānuh samyamitendriyoachaladrśā paśyedbhruvorantaram
Hyetanmokshakapātabhedajanakam Siddhāsanam prochyat

Press firmly the heel of the left foot against the perineum, and the right heel above the male organ. With the chin pressing on the chest, one should sit calmly, having restrained the senses, and gaze steadily the space between the eyebrows.

This is called the Siddha Âsana, the opener of the door of salvation.