"Living here is comfortable."
'Here' is 这里. Literally translated, 在这里 is more like '[at] here', we just don't use the 'at' in English. Similarly, 住在 isn't just 'live', but 'live at/in'.
So, 住在这里 is 'live [at] here', which is the correct way to phrase it in Chinese, but 住在在这里 is 'live [at at] here'. The duplication of 在 isn't needed.