In the Himalayas, there is a pool called Indradyumna. Akupara is a tortoise that lives here. There is a belief that this is the first ever tortoise. The Mahabharata Vanaparva Chapter 199 has a description of him.

During the Pandavas’ stay in the forest, the sage Markandeya consoled Yudhishtira with various stories. The Pandavas, and other rishis asked Markandeya whether there were any beings existed from before his time. Markandeya told them that long back, a Rajarishi called Indradyumna lost his status and fell from the heavens. He asked me whether I knew him. I told him that I didn’t, but in the Himalayas, there is a chiranjeevi owl called Pravirakarna. He might know you. On hearing this, Indradyumna took the form of a horse and carried me to the owl. But the owl told us that in the pool called Indradyumnam, there lived Nadijangha, a crane who was an older chiranjeevi than him. The crane too said that he didn’t know Indradyumna, but in the pool was a tortoise who was a chiranjeevi even older than him, called Akupara.

Indradyumna asked the tortoise if he knew him. Akupara meditated for a while, and then said, with tears in his eyes, “How could i not know you? Your acts of kindness are famous. This very river is through an act of yours. As soon as these words were said, the chariot of the gods appeared. The king got into it, and after ensuring that we were dropped back, he left for heaven.