Madhukeshwara Temple at Banavasi, Sirsi taluk , Uttara Kannada district is probably the oldest temple in Karnataka.
Banavasi is very old place, it was also called as Vaijayanthipura in ancient times.
Huan Tsang and Alberuni have mentioned this place in their works. Kannada poet Pampa had lived here.
Kadamba dynasty which is called as the first Kannada Empire, started ruling from 345 AD. They considered Madhukeshwara as their kula devata, hence this temple precedes 3rd century.
It was originally built by Shatavahanas, Kadambas developed it and later was expanded by Chalukyas and Hoysalas.
It is dedicated to Lord Shiva. Here, one can see Linga in the color of honey and hence the name Madhukeshwara, madhu meaning Honey in Kannada and Sanskrit.
The east facing temple has shrines of Mahisasuramardhini, Ganesha, Nandi statue, and an ornamented shikara. The other temples found in the complex are dedicated to Parvati, Veerbhadreshwara, Narasimha, and Basavalingeshwara.
The precinct is full of sculptures taking different forms of deities placed in smaller temples of the courtyard. You can also Naga sculpture with an inscription in Brahmi and Prakrit.
There is a Nandi statue placed in Nritya Manatpa. It is about 7 feet huge and it is positioned in a way that it looks Shiva with the left eye and Parvathi with the right one.
Banavasi was the first capital of Karnataka.
Ending this answer with Pampa’s quote about Banavasi.
ಮಱದುಂಬಿಯಾಗಿ ಮೇಣ್ ಕೋಗಿಲೆಯಾಗಿ ಪುಟ್ಟುವುದು ನಂದನದೊಳ್ ವನವಾಸಿ ದೇಶದೊಳ್|
Translation in English -
It is a virtue to be born in Banavasi as a human being. If not as a human being, then one should be born at least as a bee or a cuckoo in the garden of Banavasi.