Traveling to Kochi and Alleppey to visit family. I'm especially interested in visiting sites of historical and archeological importance and would love some recommendations.

Hi all. I'm traveling from the states to visit my Ammachi. I was hoping to squeeze in some sight-seeing during my travels and have a particular interest in ancient and historical sites in and around Kochi and Alleppey (& I suppose also Munnar, which we will be visiting for 2-3 days). My family is Christian, so I'd love to check out some of the older / more significant churches in either location. I also am curious about visiting hindu temples while I'm here -- is that something permitted or taboo if you are not hindu, or is there generally an openness about these things?

Thank you all & please forgive my ignorance in these matters.