From the wiki article:
Hundreds of years ago, it is said, that there was a kingdom called Nandavara on the banks of the river Tunga in Karnataka near Raichur district, or another namesake village Nandavaram located in the Banaganapalle mandal of the Kurnool district of Andhra Pradesh. According to a legend the king of Nandavara was a Shakti Upasaka. With the help of Mantra Shakti, the king used to wake up at 4 'O' Clock in the morning, reach Kasi, bathe, in the holy Ganga and return to his Kingdom before dawn and offer worship to Devi at Nandavara. This was his daily practice. Maharani becoming suspicious of his absence and questioned the king. The king revealed everything in detail. She having made up her mind to test the king compelled him to take her also with him. The king reluctantly accepted. The next day, he took her to Kasi along with him. Rani had her monthly course during their stay at Kasi. This affected the king and he lost his Mantra Shakti. As he was unable to return to his kingdom as usual, the King became restless and worried.
I am interested in knowing which "Mantra Shakti" the king was using for his daily rituals as mentioned in above bold part of paragraph ?