Here is the official facebook invite for August 19: https://www.facebook.com/events/1775886942638235/
bb11 - you are most certainly welcome. I'd guess about a third of the group are atheists.
On the topic of August 22 hiking, I started writing some ideas and this ended up as a download of some of my best hiking trips inside and outside of NYC. Hope it's useful (and I'd be interested in other peoples' lists), although this does nothing to narrow down a location for August 22.
On Metro North (downside is the tickets are $10-20 per person):
1) Beacon NY - you can walk through town from the Metro North station to the Beacon Mountain trail head. Challenging, beautiful hike.
2) Appalachian Trail - A couple of Metro North trains stop at the AT on weekends. This is a relatively easy hike.
3) Sleepy Hollow/Ossining NY - There is an Aqueduct Trail running through several towns on the Hudson River. The stretch from Ossining to Sleepy Hollow is one of the best bits. I recommend starting in Ossining so you can hang out in Sleepy Hollow after the walk. This is a pretty walk but not challenging since the trail is flat.
Inside NYC (more crowded, but cheaper):
4) Fort Tyron Park - Lovely park at the north of Manhattan with good hiking trails. I did this in the very early spring, so I'm not sure how crowded it is in the summer.
5) Central, Prospect, and Riverside Park all have nice 'wilderness' areas. This doesn't quite qualify as hiking, but each park is lovely.
6) Pelham Bay Park in the Bronx has nice trails
Other cool cheap things to do:
7) Free kayaking is often just paddling around in a circle, but the LIC Boathouse also sponsors free kayaking expeditions. I've done a bunch of trips with this group and it's downright extraordinary to see the city from the water.
8) Governor's Island - Fun, quirky, great place for a picnic