Matsya Purana 119.6

119.6

tathāpi divasākāraṃ prakāśaṃ tadaharniśam.
krośādhikaparīmāṇaṃ sarasāca virājitam.. 119.6 ..

About 400 cubits (palva) of that cave was enveloped in darkness, and further off, it was full of light of its own, where there was a dome-like round place, very high and sombre. The sun and the moon did not shine there.—4-5. It was bright like the day time, all night and day (probably owing to the presence of radium there) and there was a beautiful lake, more than 2 miles in length.—6.