Too late to edit, want to clarify that I mean a locally-hosted instance elsewhere on the network. When the HN is in AP mode and you connect to its AP, you're connecting to an instance hosted on the HN itself, which of course is local. I'm interested in an instance elsewhere on the network, where I can manage my own DNS.
Edit: It's likely that you can connect to the AP, use dig/nmap/tshark to determine where the local instance is (likely just the HN's IP on port 80/443), set that hosts entry in your router/DNS server, and connect to it via the hostname you set from the internet-less wifi network. However, I will not be attempting this nor will I be doing any analysis with external utilities until getting explicit approval from HN. If
@HexNailAva wants to approve of the above method, I'd be happy to create a tutorial for setting this up. So long as the webserver is running on the HN even when it's connected to another network, this should work and it would allow
@ensabbahnur to do what he needs at festivals. The hosts entry doesn't even need to be on the router or DNS server; it can be on the connecting device (phone/tablet/laptop) itself.
@muunch The Surface Pro 2 is a great device to get for the money, but it's WAY overkill for a dedicated HN device. All you need is a touchscreen, wifi, and a browser. I would get a used android tablet off ebay or craigslist for $50. If you want something new, I'd check out dhgate; they have a large variety of tablets/phablets that fit your needs and are <$50 new.
If you look hard enough on ebay and don't mind scratches, there are plenty of more-reputable tablets (Samsung Galaxy Tab models for example) to choose from for under $50, including tablets that are still supported on XDA (which I know you're into).