Someswaram or Kotipalli (Kumararama) is an important pilgrimage center in coastal Andhra Pradesh, located near Rajahmundry. Kotipalli finds mention in the Brahmananda and Gowtami puranas.  It is unique for the presence of both Shiva and Vishnu shrines in the same temple.  Shiva is worshipped here as Someswara, while Vishnu is worshipped as Sri Janardhana Swamy.  The temple is known as Sri Someswara Swamy/Sri Janardhana Swamy temple.

Kotipalli or Koti Theertham is located at confluence of the river Godavari with the sea. At the origin of the river is the Tryambakeshwar Jyotirlinga shrine in Maharashtra. The river Godavari is revered as one of the gifts of nature and is held in great regard both at its origin Triambakeshwar and at its confluence with the ocean. Thus, worship at Someswaram or Kotipalli is closely associated with a ritual bath in the river Godavari.

Legend has it that when Lord Subramanya killed the demon Tarakasura, the Shivalingam in his throat broke and fell in five different spots, which became the Pancharama kshetras. The foremost of these is Amareswara at Amaravati where Indra and the Devas are believed to have worshipped Shiva.  The others are Draksharama, Kumararama at Kotipalli, Bheemarama at Samalkota and Ksheerarama or Palakollu.

Yet another legend links the pancharama kshetras. The five Shivalingams worshipped at these shrines are said to be a part of a single Shivalingam said to have been created by Surya or the Sun God. This original Shivalingam is said to have been held in worship by the seven rishis (sages) – Kasyapa, Atri, Gowtama, Kousika, Bharadwaja, Vasishta and Jamadagni. These rishis are believed to be present in the seven tributaries of Godavari, of which the Bharadwaja, Kousika and Jamadagni Godavaris are not in existence anymore. It is believed that the seven rishis brought water into the Godavari River from their points of origin. It is also believed that the waters from the seven tributaries constitute the water sources in the temple tank.

For time immemorial it has been believed that a ritual bath in the river Godavari at Kotipalli is symbolic of a new beginning in life, a change in direction, of forgiveness of heinous sins committed by repentant souls especially in the month of Kartika, and on Maha Shivaratri. Every day in the early hours the Abhishekam for the Lord is done with this Koti Theertham water which is brought by Archakas (priests).

Shiva is worshipped here as Someswara Swamy or Koteeshwara Swamy and his consort Parvati as Rajarajeswari Devi. Here there are three famous idols which have been installed and established by Lord Indra, Lord Chandra and Kashyapa Maharshi.

Siddhi Janardhana Swamy along with Sridevi and Bhudevi were established as Kshetra Palaka by Kashyapa Maharshi.

Lord Indra in order to wash away his sin installed Koteswara Lingam, which is a Yoga Lingam, along with Sri Rajarajeswari Devi.

Further Lord Chandra established Sri Someswara Lingam, which is a Bhoga Lingam, with Sri Ananpurna Devi to wash away his sin.

Legends 

Legend has it that the moon God Chandra was cursed by Daksha to lose his brilliance and that he was relieved of his curse after he offered worship to Shiva at Koti Theertham at the mouth of the river Godavari.

According to another legend, Gowtama believed to be one of the foremost sages of ancient India was married to Ahalya. Indra the king of the Devas lusted after Ahalya and using a ploy, diverted Gowtama and assuming the disguise of Gowtama led Ahalya in his embrace. An enraged sage cursed his wife who petrified into a rock immediately and was absolved of her curse by Rama (incarnation of Vishnu). Indra the king of Devas was cursed with a life of disease. Legend has it that he lived through his curse and performed severe penances (at the instance of Gowtama rishi) and finally was absolved of his curse and forgiven when his penance concluded with a ritual dip in the Godavari River at Someswaram.

In the premises of the temple there are four Pradakshina Mandapams. In this Mandapams there is a Kalabhairava Swamy temple and Shankaracharya Mandir along with Chandra Mouliswara Lingam, and a Navagraha temple along with Uma Sametha Mrityunjaya Lingam.

There is a temple tank (Koneru) in front of the temple which is known as Soma Pushkarini.

Festivals 

The worship at this temple, is associated with a ritual bath in the river, especially during Kartika & Mahashivratri.

Every year there are some festivals and events which are celebrated with great pomp and gaiety. They are: Magha Bahula Chaturdashi also known as Maha shivaratri which is celebrated in the month of Feb/Mar, Sri Swami Vari Kalyanam (Visakha Suddha Ekadashi) celebrated in the May, Navarathri festival (Aswayuja Suddha Padyami to Dwadashi) celebrated in the month of October), and Ksheerabdi Dwadashi Teppotsavam (Float Festival) during Kartika Masam also known as the month of November.

Source:

http://www.inkakinada.com/topstories/kotipalli

https://pilgrimaide.com/kotipalli-someswara-swamy-temple-.html

https://mountainvalley.in/kotipalli-temple.html

http://www.oneindiaonline.com/kotipalli.php

http://www.jyotirlinga.com/pancharama-kshetra.html

https://en.wikipedia.org/wiki/Kotipalli