Vardhamāna Dvāra was a gate of Hastināpura. Dhṛtarāshṭra left the city through this gate when he began his vānaprastha (the forest stage of life). Vidura and Sañjaya went with him, and the sorrowing people of Hastināpura followed behind.

Departure of Dhṛtarāshṭra

Dhṛtarāshṭra steadied his mind and went forward with great difficulty along the royal road. The road was crowded with weeping men and women of every varṇa. He passed out of Hastināpura through the Vardhamāna Dvāra. Again and again as he went, he turned back the crowds of citizens who wanted to follow him further.

At this gate Vidura, the mahāmātra (chief attendant), and Sañjaya, the sūta (charioteer and counsellor of the Kuru court) and son of Gavalgaṇa, took their own vows to go with the king into the forest. The Mahābhārata tells this in Āśramavāsika Parva, Chapter 16.

Sources

Mahābhārata, Āśramavāsika Parva, Chapter 16