Combining 2 different subnets

Hi, i've stumbled upon a thought that leads to this question that may sound impossible, but just wanna give it a shot. so for the IT wizz out there, please enlighten me.

If I'm running a company, and I have this network im already using that connects through the server network and to the internet. Lets just call the server 192.1.xxx.xxx. On the other hand, I will have guest visiting my company for meetings and they need to connect to the internet for business purposes as well. I don't want them to infect my server with viruses they have within their laptops. So, i created another subnet just for them for their internet access, 192.168.xxx.xxx.

I know it's not possible for them to view what i have in my server since its under a different subnet. The question is here, is there a way for the 192.168 subnet to connect to 192.1. , but setting a firewall between them so the virus doesnt trespass into my server?