Arkpocalypse

Summary
Arkpocalypse is Survival modpack built mostly around Zombies and The Lost Cities. Spawn into an apocalyptic and grim world starting deep underground in your bunker. Make your way up to a dark and dingy surface teeming with deadly creatures. Watch your health, thirst and temperature while scavenging for materials to survive the deadly hoard. Go from a struggling to survivor to a post apocalyptic hero by crafting strong weapons and base defences in the form of various guns and turrets.  

Recommendations:
I recommend using the "The Last Days" resource/texture pack - https://www.9minecraft.net/last-days-resource-pack/ this really helps darken the atmosphere. 
You can use OptiFine but it will mess with the fog effects that are in the modpack. If you do not care about the fog then no worries, OptiFine works great.