Here’s a little bit of what you can expect to find at Mariel Underground: flaming cocktails, near nightly DJs, and $5,000 bottles of champagne. That may or may not be your scene (it certainly isn’t always ours), but there are few places like it in Boston, and that alone makes it useful. Head here in the pre-club after-work hours if you just want to enjoy the selection of cocktails and very good Cuban small plates without ending up in the background of roughly 536 selfies.