How to tell if there are currently any long running queries executing? (Related to this question)

If I want to see if there are currently any long-running queries executing on my database, what's the easiest way of checking?  (I expect the answer will be some query on master..sysprocesses?)
WhoIsActive from Adam Machanic is an excellent tool/sp to see what's currently happening on your server.

The below tutorial from Brent Ozar shows how to periodically log sp_whoisactive to a table for later analysis.

https://www.brentozar.com/responder/log-sp_whoisactive-to-a-table/