Falasarna Beach
Falasarna beach is a beautiful sandy beach stretching for several km. Several areas with umbrella + 2 beach chairs at reasonable price (8-10 eur/day). Nudist area in the north side. Lots of restaurants and bars along the beach. At the top northern tip, you can visit the ancient Falasarna ruins (with internet tour IIRC) - a port destroyed by a powerful earthquake a long time BC. Free visit. Falasarna can be reached by car or bus from Kolymbari.

Gramvousa and Balos Beaches
Take a boat trip to Gramvousa beach and Balos beach. These are located in the northern tip of the westernmost Cretan peninsula. Take boat from Kissamos port (reachable by bus from Kolymbari in approx. 30'). Balos beach (picture below) can also be reached by car + 15' easy trek.
Elafonissi Beach
Located in the western-southern edge of Crete, this beach (with associated islet, reachable by feet through a 0.5m-deep passage) is famous for its pink sand. Reachable by car or bus from Kolymbari (approx. 1h). Lots of tourist structures there, restaurants etc.

Afrata Beach
Afrata Beach is about 6km from the conference center and is perfect for an afternoon.
Gramvousa Restaurant
Gramvousa restaurant is located close to Kissamos (road to Gramvousa peninsula). Amazing food. Cannot reserve, but while you wait you are served refreshments and appetizers in the garden.
Port of Chania
The port is usually full with activities, like art exhibitions and live music. Lots of shopping areas in the center. The archaeological museum is also worth a visit.
Samaria Gorge
Tak a trek in the Samaria gorge. You can walk down the amazing natural landscape of the gorge for up to 7 hours (if you take the full path). https://samaria-gorge.gr/
Bike Trails
The local Kolumbari bike rental also lists of bike hikes ranked by difficulty etc, https://bikeproject.gr/en/home/ Renting a bike is easy.
Thanks!
Many thanks to Tomasso and Pietro for the above information. If others have anything to add, please send an email to gwatts@uw.edu!