There are two houses...you can buy a ticket for just the main house or for a little more $$, a ticket for both houses. The extra for both is worth it. Escape rooms and other things are separate tickets.
Yes the general admission ticket will get you into the main attraction parking is free but if you want to do other things there such as the escape room zombie hunt etc they are extra.
There are multiple tickets for different things at netherworld, the main so called event comes with the purchase of the general admission ticket
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