The official currency in Nepal is the Nepalese Rupee (NPR). You can exchange currency at banks or authorized exchange centers. One such center is available at the airport but please note that opening hours are variable. Also, you can exchange currency at the venue of the retreat or any other exchange office in Kathmandu.
ATMs are widely available in Kathmandu for withdrawing local currency. Look for one close to a bank for the best value. There is an ATM at the airport too. Cash withdrawals are usually limited, and your account will be charged 500 Rs per withdrawal.
Credit Cards are only used in hotels or restaurants patronized by tourists. A charge of 3% (local bank charge) will be applied to all credit card payments.
The Nepalese Rupee is non-convertible, and only available in Nepal itself.
Here is an updated Currency converter: https://www.xe.com/currencyconverter
Cash for Small Expenses: Carry Nepalese rupees for small purchases, tips, and transportation.