The Cosmos object exposes a rest(network) method that allows you to call RPC methods exposed through HTTPS. RPC endpoints are mapped directly to the REST API object structure: 
import { Cosmos } from '@apophis-sdk/cosmos';

const network = await Cosmos.getNetworkFromRegistry('neutrontestnet');

const { balances, pagination } = await Cosmos.rest(network).bank.v1beta1.balances['neutron1...']('GET');
console.log(balances);

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Virtual Typing

The REST API is built on top of my @kiruse/restful library which leverages a “virtual typing” system. This means that even if an endpoint is not defined in the Apophis SDK, you can still call it using the same pattern as above. Simply refer to your chain’s OpenAPI specification and pass in the appropriate parameters. 
import { Cosmos } from '@apophis-sdk/cosmos';

const network = await Cosmos.getNetworkFromRegistry('neutrontestnet');

const api = await Cosmos.rest(network) as any;

// I genuinely have no idea if this endpoint exists, but it demonstrates the point
const { items, pagination } = await api.authz.v1beta1['neutron1...'].grants('GET');
console.log(items);