A layover at HEL.

It depends on where you're coming from and going. Connections between two Schengen-area flights stay airside with no passport check. Arriving from outside Schengen for a Schengen connection, you clear the EU's Entry/Exit System (EES) check at HEL; leaving Schengen, you clear the exit check before your gate.

LYVR shows live security wait times for each checkpoint, grouped by terminal, refreshed every couple of minutes.

LYVR shows the current queue for the EU's Entry/Exit System (EES) border checks, for both arrival and departure.

LYVR lists 6 lounges at HEL, 2 of them on Priority Pass. Which ones you can get into depends on your ticket, airline status, credit card or a lounge membership. Each lounge on this page lists what gets you in, and LYVR checks it against your own profile.

Yes, at 1 lounge: Finnair Lounge (Finnair Gold and up, oneworld Sapphire (long-haul international flights)). Status entry needs a same-day departing flight on that airline or its alliance, and some tiers only count on international flights.

It depends on your terminals, whether you re-clear security or customs, and how far the gates are apart. LYVR adds up deplaning, every walk on the indoor map, any checkpoints your connection passes and the boarding door time, then shows exactly how much time you have to spare.

Between two Schengen-area flights, often yes, since there's no passport check. Coming from or going to a country outside Schengen, you pass a border check (and register in the EU's Entry/Exit System on a first entry), which can take 30 minutes or more at busy times, so 1.5 to 2 hours is safer. LYVR works out your exact time to spare for your own two gates.

With an hour or two, eat near your gate and walk the terminal. With more, HEL's 6 lounges (2 on Priority Pass) have quiet seats, food and often showers. LYVR's Explore tab lists every restaurant, bar and shop near your gate with the walk time, so you only see what fits in your layover.

Arriving from another Schengen country, yes, with enough time. From outside Schengen, only if you're allowed to enter the Schengen area, since leaving HEL means going through immigration, and you'd want about 6 hours: the passport line both ways, the trip into Helsinki and back, and security on the way in. LYVR checks the ride each way, the time you'd have in the city and your passport's entry rule.